#include <iostream>
#include <string>
#include <cstdio>
#include <cmath>

using namespace std;

int main()
{
   double x1,x2,y1,y2;

   scanf("%lf%lf\n%lf%lf",&x1,&y1,&x2,&y2);

   printf("%.4lf",sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)));

    return 0;
}