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

struct Point { long long x, y; };
using Polygon = vector<Point>;

long long cross(Point a, Point b, Point c) {
    return (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
}

// Cat da giac boi nua mat phang (A,B)
Polygon clip(const Polygon& poly, Point A, Point B) {
    Polygon res;
    int n = poly.size();
    for (int i = 0; i < n; i++) {
        Point cur = poly[i], nxt = poly[(i + 1) % n];
        bool cur_in = cross(A, B, cur) >= 0;
        bool nxt_in = cross(A, B, nxt) >= 0;
        if (cur_in) res.push_back(cur);
        if (cur_in != nxt_in) {
            // Tim giao diem
            double t = (double)cross(A, B, cur) / (cross(A, B, cur) - cross(A, B, nxt));
            res.push_back({(long long)(cur.x + t * (nxt.x - cur.x)),
                          (long long)(cur.y + t * (nxt.y - cur.y))});
        }
    }
    return res;
}

long long polygonArea2(const Polygon& p) {
    long long s = 0;
    for (size_t i = 0; i < p.size(); i++) {
        size_t j = (i + 1) % p.size();
        s += p[i].x * p[j].y - p[j].x * p[i].y;
    }
    return abs(s);
}

long long boundaryPoints(const Polygon& p) {
    long long b = 0;
    for (size_t i = 0; i < p.size(); i++) {
        size_t j = (i + 1) % p.size();
        b += __gcd(abs(p[j].x - p[i].x), abs(p[j].y - p[i].y));
    }
    return b;
}

int main() {
    Polygon tri[3];
    for (int t = 0; t < 3; t++) {
        tri[t].resize(3);
        for (int i = 0; i < 3; i++)
            cin >> tri[t][i].x >> tri[t][i].y;
    }

    Polygon inter = tri[0];
    for (int t = 1; t < 3; t++) {
        for (int i = 0; i < 3; i++) {
            int j = (i + 1) % 3;
            inter = clip(inter, tri[t][i], tri[t][j]);
        }
    }

    if (inter.size() < 3) { cout << "0\n"; return 0; }
    long long area2 = polygonArea2(inter);
    long long B = boundaryPoints(inter);
    long long I = (area2 - B + 2) / 2;
    cout << I << "\n";
    return 0;
}