import java.io.PrintStream;
import java.util.Arrays;
import java.util.Scanner;

/**
 * Solution to Bikes and Barricades
 * 
 * @author vanb
 */
public class bikes_vanb
{
    /** Input. */
    private static Scanner sc;
    
    /** Output. */
    private static PrintStream ps;
    
    /**
     * Do it!
     */
    private void doit()
    {
        int n = sc.nextInt();
        double closest = -1.0;
        while( n-->0 )
        {
            int x1 = sc.nextInt();
            int y1 = sc.nextInt();
            int x2 = sc.nextInt();
            int y2 = sc.nextInt();
            
            // The input spec says that x1!=0, x2!=0. 
            // If x1==x2, we have a vertical line, which cannot possibly block the road.
            // If x1*x2>0, then both points are n the same side of the Y axis, the barricade cannot cross.
            if( x1*x2<0 )
            {
                // The basic equation of a line: y=mx+b! 
                // b is the Y intercept, that's what we want!
                // m is slope
                double m = (double)(y2-y1)/(double)(x2-x1);
                double b = y1 - m*x1;
                
                // Scott is going up from (0,0), so if b is negative, it won't be in his way.
                // If closest<0, it has to be -1.0, which means we haven't seen any blocking barricades yet.
                if( b>0.0 && (closest<0.0 || b<closest)) closest = b;
            }
        }
        
        ps.println( closest );
    }
        
    /**
     * Main.
     * 
     * @param args unused
     * @throws Exception
     */
    public static void main( String[] args ) throws Exception
    {
        sc = new Scanner( System.in );
        ps = System.out;
        
        new bikes_vanb().doit();
    }

}