//使用sqrt函数,需要引入cmath
#include <cstdio>
#include <cmath>
using namespace std;
int main()
{
double x1, y1, x2, y2;
scanf("%lf%lf", &x1, &y1);
scanf("%lf%lf", &x2, &y2);
printf("%.4lf", sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)));
}