#include <bits/stdc++.h>

using namespace std;

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