Untitled

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;


double distance(double x1, double y1, double x2, double y2) {
    double a = abs(x1 - x2);
    double b = abs(y1 - y2);
    return sqrt(a * a + b * b);
}

int main() {
    double  x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    cout << fixed << setprecision(5);
    cout << distance(x1, y1, x2, y2);
    return 0;
}