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

using ld = long double;

vector<ld> di = {-1, 0, 1, 0};
vector<ld> dj = {0, 1, 0, -1};

int main() {
    ld a, b, c, d, e, f;
    cin >> a >> b >> c >> d >> e >> f;
    
    auto s = [](ld a, ld b, ld c, ld d, ld e, ld f) -> ld {
        c -= a;
        d -= b;
        e -= a;
        f -= b;
        return abs(c * f - d * e) / 2.0;
    };
    
    ld ans = 0;
    for (int i = 0; i < 4; i++) {
        ld na = a + di[i], nb = b + dj[i];
        for (int j = 0; j < 4; j++) {
            ld nc = c + di[j], nd = d + dj[j];
            for (int k = 0; k < 4; k++) {
                ld ne = e + di[k], nf = f + dj[k];
                
                ans = max(ans, s(na, nb, nc, nd, ne, nf));
            }
        }
    }
    
    cout << fixed << setprecision(1) << ans << endl;
}