#include <bits/stdc++.h>
using namespace std;
#define all(v) (v).begin(),(v).end()
#define pb(a) push_back(a)
#define rep(i, n) for(int i=0;i<n;i++)
#define foa(e, v) for(auto& e : v)
using ll = long long;
const ll MOD7 = 1000000007, MOD998 = 998244353, INF = (1LL << 60);
#define dout(a) cout<<fixed<<setprecision(10)<<a<<endl;

int area(int a, int b, int c, int d, int e, int f) {
    c -= a;
    d -=b;
    e -=a;
    f -=b;
    return abs(c * f - e * d);
}
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int a, b, c, d, e, f;
    cin >> a >> b >> c >> d >> e >> f;
    int dy[4] = {-1, 0, 0, 1};
    int dx[4] = {0, -1, 1, 0};
    int ans = 0;
    rep(bit, 64) {
        vector<int> v;
        rep(i, 3) {
            int num = 0;
            num |= (bit >> (i * 2) & 3);
            v.pb(num);
        }
        ans = max(ans, area(a + dy[v[0]], b + dx[v[0]], c + dy[v[1]], d + dx[v[1]], e + dy[v[2]], f + dx[v[2]]));
    }
    if(ans & 1) cout << ans/2 << ".5" << endl;
    else cout << ans/2 << endl;
    return 0;
}