#include <bits/stdc++.h>

using namespace std;
void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int area(vector<int> x) {
    int x1 = x[0], y1 = x[1], x2 = x[2], y2 = x[3], x3 = x[4], y3 = x[5];
    return abs((x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)));
}
int main() {
    fast_io();
    vector<int> x(6);
    for (int i = 0; i < 6; i++) {
        cin >> x[i];
    }
    int ans = 0;
    for (int s = 0; s < (1 << 6); s++) {
        vector<int> y(6);
        for (int i = 0; i < 6; i++) {
            y[i] = x[i];
        }
        for (int i = 0; i < 3; i++) {
            int op = s >> (2 * i);
            op %= 4;
            if (op == 0) {
                y[2 * i]++;
            } else if (op == 1) {
                y[2 * i + 1]++;
            } else if (op == 2) {
                y[2 * i]--;
            } else {
                y[2 * i + 1]--;
            }
        }
        ans = max(ans, area(y));
    }
    cout << (double)ans / 2 << endl;
}