#include <cstdio>
#include <cmath>
using namespace std;

int main()
{
    double x1,y1,x2,y2;
    while(~scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2))
        printf("%.2lf\n",sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)));
    return 0;
}