#include <bits/stdc++.h>
using namespace std;
double sqr(double x) {
return x * x;
} double line(double xa,double ya, double xb,double yb) {
double a = sqr(xa - xb);
double b = sqr(ya - yb);
return sqrt(a + b);
} int main() {
double xa,ya, xb, yb;
cin >> xa >> ya;
cin >> xb >> yb;
double len = line(xa, ya, xb, yb);
cout << fixed << setprecision(3) << len;
return 0;
}