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

using namespace std;

int main(){
    double x1, y1, x2, y2, d1, d2, distance;
    cin>>x1>>y1>>x2>>y2;
    d1 = pow(x1 - x2, 2);
    d2 = pow(y1 - y2, 2);
    distance = sqrt(d1+d2);
    printf("%.4lf", distance);
    return 0;
}