#include <bits/stdc++.h>

using namespace std;

int main() {
    double x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    cout << fixed << setprecision(4) <<  sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2)) << endl;
    return 0;
}