#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
int main() {
  int a, b, c, d, e, f;
  cin >> a >> b >> c >> d >> e >> f;
  printf("%.10f\n", sqrt(f - e + c * c / 4.0 + d * d / 4.0));
  return 0;
}