import java.awt.Point;
import java.util.*;
public class e {
	Scanner in=new Scanner(System.in);
	public static void main(String[] args) {
		new e().go();
	}
	private void go() {
		while(true){
			int[] d=new int[8];
			for(int i=0;i<8;i++)d[i]=in.nextInt();
			if(d[0]==d[2])break;
			boolean aon=d[4]>=d[0]&&d[4]<=d[2]&&d[5]>=d[1]&&d[5]<=d[3];
			boolean bon=d[6]>=d[0]&&d[6]<=d[2]&&d[7]>=d[1]&&d[7]<=d[3];
			if(aon&&bon){//both on the grid
				System.out.printf("%.3f\n",(double)Math.abs(d[7]-d[5])+Math.abs(d[6]-d[4]));
				continue;
			}
			if(aon){//if aon the grid, flip the points for simplicity
				int temp=d[5];
				d[5]=d[7];
				d[7]=temp;
				temp=d[4];
				d[4]=d[6];
				d[6]=temp;
			}
			if(aon||bon){//if one left on grid, iterate through all points visible to other
				double min=Double.MAX_VALUE;
				if(d[4]<d[0])for(int i=d[1];i<=d[3];i++)min=Math.min(min, Math.sqrt(Math.pow(d[4]-d[0], 2)+Math.pow(d[5]-i, 2))+Math.abs(d[7]-i)+Math.abs(d[6]-d[0]));
				if(d[4]>d[2])for(int i=d[1];i<=d[3];i++)min=Math.min(min, Math.sqrt(Math.pow(d[4]-d[2], 2)+Math.pow(d[5]-i, 2))+Math.abs(d[7]-i)+Math.abs(d[6]-d[2]));
				if(d[5]<d[1])for(int i=d[0];i<=d[2];i++)min=Math.min(min, Math.sqrt(Math.pow(d[4]-i, 2)+Math.pow(d[5]-d[1], 2))+Math.abs(d[6]-i)+Math.abs(d[7]-d[1]));
				if(d[5]>d[3])for(int i=d[0];i<=d[2];i++)min=Math.min(min, Math.sqrt(Math.pow(d[4]-i, 2)+Math.pow(d[5]-d[3], 2))+Math.abs(d[6]-i)+Math.abs(d[7]-d[3]));
				System.out.printf("%.3f\n",min);
				continue;
			}
			int count=0;
			count+=cross(d[4],d[5],d[6],d[7],d[0],d[1]);
			count+=cross(d[4],d[5],d[6],d[7],d[0],d[3]);
			count+=cross(d[4],d[5],d[6],d[7],d[2],d[1]);
			count+=cross(d[4],d[5],d[6],d[7],d[2],d[3]);
			if((d[4]>=d[2]&&d[6]>=d[2])||(d[4]<=d[0]&&d[6]<=d[0])||(d[5]>=d[3]&&d[7]>=d[3])||(d[5]<=d[1]&&d[7]<=d[1])||Math.abs(count)==4){//straight line (either both left or right up or down of whole thing, or crossproduct to each corner is the same
				System.out.printf("%.3f\n",Math.sqrt(Math.pow(d[7]-d[5],2)+Math.pow(d[6]-d[4],2)));
				continue;
			}
			double min=Double.MAX_VALUE;//both off, no straight line, iterate over all points visible to each one
			ArrayList<Point> a=new ArrayList<Point>(),b=new ArrayList<Point>();
			if(d[4]<d[0])for(int i=d[1];i<=d[3];i++)a.add(new Point(d[0],i));
			if(d[4]>d[2])for(int i=d[1];i<=d[3];i++)a.add(new Point(d[2],i));
			if(d[5]<d[1])for(int i=d[0];i<=d[2];i++)a.add(new Point(i,d[1]));
			if(d[5]>d[3])for(int i=d[0];i<=d[2];i++)a.add(new Point(i,d[3]));
			if(d[6]<d[0])for(int i=d[1];i<=d[3];i++)b.add(new Point(d[0],i));
			if(d[6]>d[2])for(int i=d[1];i<=d[3];i++)b.add(new Point(d[2],i));
			if(d[7]<d[1])for(int i=d[0];i<=d[2];i++)b.add(new Point(i,d[1]));
			if(d[7]>d[3])for(int i=d[0];i<=d[2];i++)b.add(new Point(i,d[3]));
			for(Point aa:a)for(Point bb:b)min=Math.min(min, Math.sqrt(Math.pow(d[5]-aa.y,2)+Math.pow(d[4]-aa.x,2))+Math.sqrt(Math.pow(d[7]-bb.y,2)+Math.pow(d[6]-bb.x,2))+Math.abs(aa.x-bb.x)+Math.abs(aa.y-bb.y));
			System.out.printf("%.3f\n",min);
		}
			
	}
	private int cross(int i, int j, int k, int l, int m, int n) {
		int tmp=(k-i)*(n-j)-(m-i)*(l-j);
		if(tmp==0)return 18;
		return tmp/Math.abs(tmp);
	}
}
//Extended Manhattan Distance
//cross products
//case work