杭电2001

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