#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  vector ps(3, vector<ll>(2, 0));
  rep(i, 3) rep(j, 2) cin >> ps[i][j];
  auto dfs = [&](auto self, ll i) -> ll {
    if (i == 3) {
      ll x1 = ps[1][0] - ps[0][0];
      ll x2 = ps[2][0] - ps[0][0];
      ll y1 = ps[1][1] - ps[0][1];
      ll y2 = ps[2][1] - ps[0][1];
      return abs(x1 * y2 - x2 * y1);
    }
    ll res = 0;
    rep(j, 2) for (const auto d : {-1, 1}) {
      ps[i][j] += d;
      res = max(res, self(self, i + 1));
      ps[i][j] -= d;
    }
    return res;
  };
  ll ans = dfs(dfs, 0);
  cout << ans / 2 << '.' << (ans % 2 ? '5' : '0') << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}