URI_1015.cpp

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

int main (){
    double x1, x2, y1, y2, distancia;

    cin >> x1 >> y1;
    cin >> x2 >> y2;

    distancia = (( (x2 - x1) * (x2 - x1) ) + ((y2 - y1) * (y2 - y1)));

    cout << fixed << setprecision (4) << sqrt (distancia) << endl;

    return 0;
}