aaa

#include <iostream>
#include <cstdio>
#include <cmath>

using namespace std;

int main(void) {
    int a, b, c, d;
    float s;
    cin >> a >> b >> c >> d;
    s = (float)sqrt((pow((a - c), 2) + pow((b - d), 2)));
    printf("%.2lf", s);
    return 0;
}