#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main()
{
double x1, y1;
double x2, y2;
double distance;
scanf("%lf%lf",&x1,&y1);
scanf("%lf%lf",&x2,&y2);
distance = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
printf("%.4lf",distance);
return 0;
}