杭电2001

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
int main()
{
    double x1,x2,y1,y2,s;
    while(scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2)!=EOF)
    {
         s=sqrt(((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
         printf("%.2lf\n",s);
    }
   // system("pause");
    return 0;
}