#include <iostream>
#include <cmath>
using namespace std;
signed main(){
double x1, x2, y1, y2;
cin >> x1 >> x2 >> y1 >> y2;
cout << sqrt(pow(x2-x1,2) + pow(y2-y1,2));
}
#include <iostream>
#include <cmath>
using namespace std;
signed main(){
double x1, x2, y1, y2;
cin >> x1 >> x2 >> y1 >> y2;
cout << sqrt(pow(x2-x1,2) + pow(y2-y1,2));
}