#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    double a, b, c, d, e, f;
    cin >> a >> b >> c >> d >> e >> f;

    c *= -0.5;
    d *= -0.5;
    f += c * c + d * d - e;

    printf("%.15f\n", sqrt(f));

    return 0;
}