tijie

#include <bits/stdc++.h>
using namespace std;
double ecld(double a, double b, double c, double d){
    return sqrt((a - c) * (a - c) + (b - d) * (b - d));
}
int main(){
    double a, b, c, d;
    cin >> a >> b >> c >> d;
    printf("%.2lf", ecld(a, b, c, d));
    return 0;
}