import java.io.*;
import java.util.*;
import java.awt.*;

/**
 * Solution to Tsunami
 * 
 * @author vanb
 */
public class tsunami
{
    public Scanner sc;
    public PrintStream ps;
    
    /**
     * This will hold the parameters of a cable: an index of eacg
     * of the two endpoints, and its length.
     */
    public class Cable implements Comparable<Cable>
    {
        public int a, b;
        public double distance;
        
        /**
         * Create a Cable
         * @param a Index of an endpoint
         * @param b Index of the other endpoint
         * @param distance Length
         */
        public Cable( int a, int b, double distance )
        {
            this.a = a;
            this.b = b;
            this.distance = distance;
        }
        
        /**
         * Compare two Cables by distance.
         * 
         * @param c Cable to compare to this Cable
         * @return -1, 0 or 1, just like a standard compareTo method.
         */
        public int compareTo( Cable c )
        {
            return Double.compare( distance, c.distance );
        }
        
        /**
         * Produce a pretty string for debugging.
         */
        public String toString()
        {
            return "{a=" + a + ", b=" + b + ", distance=" + distance + "}";
        }
    }
    
    // The link[] array will help us manage the sets we'll use
    // for Kruskal's MST algorithm.
    public int parent[] = new int[1000];
    
    // This is the minimum y value of a set of cities
    public int miny[] = new int[1000];
    
    /**
     * Figure out which set city i is in.
     * 
     * We'll maintain each set as a tree, with each node linked to its parent.
     * We'll use the index of the root node of the tree as a unique identifier
     * for the set.
     * 
     * @param i City index
     * @return Indicates which set i is in.
     */
    public int set( int i )
    {
        // Find the root (that's where parent[i]==-1)
        while( parent[i]>=0 ) i=parent[i];
        return i;
    }
    
    /**
     * Merge the set that i is in with the set that j is in.
     * 
     * @param i City
     * @param j Another city
     */
    public void merge( int i, int j )
    {
        // Get the root of i's tree, which identifies its set
        i = set(i);
        
        // Look for the root of j's tree
        while( parent[j]>=0 )
        {
            int t = j;
            j = parent[j];
            
            // On our way up, we'll do some surgery on the tree.
            // We'll point these nodes directly to the root.
            // We're only interested in the root anyway, so this
            // does no harm, and it can speed us up if we come looking
            // for one of these nodes later.
            parent[t] = i;
        }
        
        // Put this subtree under i
        parent[j] = i;
        
        // The minimum y of this new merged set is
        // the minimum of the y's of the two sets we're merging
        miny[i] = Math.min( miny[i], miny[j] );
    }
    
    /**
     * Driver.
     * @throws Exception
     */
    public void doit(String filename) throws Exception
    {
        sc = new Scanner( new File( filename ) );
        ps = System.out; //new PrintStream( new FileOutputStream( "tsunami.out" ) ); 
                        
        Point cities[] = new Point[1000];                
        PriorityQueue<Cable> queue = new PriorityQueue<Cable>();
        
        // We'll use a modification of Kruskal's algorithm to find a
        // Minimum Spanning Tree.
        //
        // Kruskal's algorithm goes like this: Start with each node in its own set.
        // If you've got n nodes, then you've got n sets. Then, sort all of
        // edges by weight (in this case, length or distance) Go through the edges,
        // smallest to largest. If an edge connects two nodes that are in difference sets,
        // then union those two sets, and add that edge to the Minimum Spanning Tree. 
        // (Obviously, if the two nodes are in the same set, then we don't need that edge.
        // Just pass it by.) That's all there is to it!
        for(;;)
        {
            int n = sc.nextInt();
            if( n==0 ) break;
            
            // At the beginning, every city is in its own set.
            Arrays.fill( parent, -1 );
            
            for( int i=0; i<n; i++ )
            {
                int x = sc.nextInt();
                int y = sc.nextInt();
                cities[i] = new Point( x, y );
                
                // The miny of every city is its own y, since
                // every city is in its own set.
                miny[i] = y;
            }
            
            // Put every edge on a Priority Queue, 
            // sorted by minimum distance
            for( int i=0; i<n; i++ ) for( int j=i+1; j<n; j++ )
            {
                queue.add( new Cable( i, j, cities[i].distance( cities[j] ) ) );
            }
            
            // Go through the queue, smallest to largest
            double total = 0.0;
            while( !queue.isEmpty() )
            {
                Cable cable = queue.poll();
                int a = cable.a;
                int b = cable.b;
                int sa = set(a);
                int sb = set(b);
                
                // If the two cities are in different sets
                if( sa != sb )
                {
                    // Here's where we deviate from Kruskal a bit.
                    // We can only use this edge under certain circumstances.
                    //
                    // Suppose the edge looks like this:
                    //  a
                    //   \
                    //    \
                    //     b
                    // Think about all of the nodes that are in a's set. 
                    // They're all already connected with edges - that's why they're 
                    // in the same set. If any one of them has a smaller y than a, then
                    // we risk sending the warning up to a, and then back down again to
                    // that lower city. We can't do that. So, if a has the higher y of the 
                    // edge, then a's y must be the minimum y of all of the nodes in a's set.
                    // Ditto for b - if it has the larger y, then that y value must be the
                    // minimum y of all of the cities in b's set. If a.y == b.y, then
                    // all we require is that ONE of them be the minimum of their set.                    
                    boolean ok = false;
                    
                    // a is OK if it's the lowest city in its set
                    boolean oka = (cities[a].y==miny[sa]);
                    
                    // Ditto for b
                    boolean okb = (cities[b].y==miny[sb]);
                    
                    // If a is the highest endpoint of this
                    // edge, then it must be the lowest city in its set.
                    if( cities[a].y > cities[b].y )
                    {
                        ok = oka;
                    }
                    // Ditto for b.
                    else if(cities[a].y < cities[b].y)
                    {
                        ok = okb;                        
                    }
                    // If they're equal, then using this edge is OK if either a or b is OK.
                    else
                    {
                        ok =  oka || okb;
                    }
                    
                    // If OK, use this edge.
                    if( ok )
                    {
                        // Merge the sets, record the distance.
                        merge( a, b );
                        total += cable.distance;
                    }
                }
            }
            
            ps.printf( "%.02f", total );
            ps.println();
        }
    }
    
    /**
     * @param args
     */
    public static void main( String[] args ) throws Exception
    {
        new tsunami().doit(args[0]);
    }

}