#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int _a, _b, _c, _d, _e, _f;
  cin >> _a >> _b >> _c >> _d >> _e >> _f;
  int ans = 0;
  rep(bit, 0b1111'1111'1111 + 1) {
    int xbit = (bit >> 0) & 0b1111;
    int ybit = (bit >> 4) & 0b1111;
    int zbit = (bit >> 8) & 0b1111;
    if (popcount(ull(xbit)) != 1 || popcount(ull(ybit)) != 1 || popcount(ull(zbit)) != 1) continue;
    int a = _a + (xbit & 0b0010 ? 1 : 0) - (xbit & 0b0001 ? 1 : 0);
    int b = _b + (xbit & 0b1000 ? 1 : 0) - (xbit & 0b0100 ? 1 : 0);
    int c = _c + (ybit & 0b0010 ? 1 : 0) - (ybit & 0b0001 ? 1 : 0);
    int d = _d + (ybit & 0b1000 ? 1 : 0) - (ybit & 0b0100 ? 1 : 0);
    int e = _e + (zbit & 0b0010 ? 1 : 0) - (zbit & 0b0001 ? 1 : 0);
    int f = _f + (zbit & 0b1000 ? 1 : 0) - (zbit & 0b0100 ? 1 : 0);
    int s = b * c - f * c - a * d - b * e + d * e + a * f;
    ans = max(ans, s);
  }
  cout << ans / 2;
  if (ans % 2) cout << ".5";
  cout << endl;
  return 0;
}