cout << sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));

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

int main()
{
   double x1, y1, x2, y2;
   cin >> x1; cin >> y1; cin >> x2; cin >> y2;
   cout << sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
}