#include<stdio.h>
#include<math.h>
using namespace std;
int main()
{
    double x1,y1,x2,y2;    
    char d;
    while(scanf("%lf%lf%lf%lf%c",&x1,&y1,&x2,&y2,&d)!=EOF)
    {
        double a;
        a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        printf("%.2lf\n",a);
    }
}