#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)n; i++)

int main() {
  vector<int> x(3), y(3);
  rep(i, 3)
    cin >> x[i] >> y[i];
  auto s2 = [&](vector<int> x, vector<int> y) {
    rep(i, 2) {
      x[i+1] -= x[0];
      y[i+1] -= y[0];
    }
    x[0] = 0, y[0] = 0;
    return abs(x[1] * y[2] - x[2] * y[1]);
  };
  int ans = 0;
  vector<int> dx = {1, -1, 0, 0};
  vector<int> dy = {0, 0, 1, -1};
  auto dfs = [&](auto dfs, int i, vector<int> x, vector<int> y) {
    if (i == 3) {
      ans = max(s2(x, y), ans);
      return;
    }
    rep(j, 4) {
      x[i] += dx[j];
      y[i] += dy[j];
      dfs(dfs, i + 1, x, y);
      x[i] -= dx[j];
      y[i] -= dy[j];
    }
    return;
  };
  dfs(dfs, 0, x, y);
  cout << fixed << setprecision(1) << (float)ans / 2 << endl;
  return 0;
}