геома

typedef long double ld;

struct vect {
    ld x, y;
    vect(): x(0), y(0) {}
    vect(ld x, ld y): x(x), y(y) {}
    vect(vect a, vect b): x(b.x - a.x), y(b.y - a.y) {}
};

vect operator+(vect a, vect b) {
    return vect(a.x + b.x, a.y + b.y);
}

ld operator*(vect a, vect b) {
    return a.x * b.x + a.y * b.y;
}

vect operator*(vect a, ld k) {
    return vect(a.x * k, a.y * k);
}

ld operator^(vect a, vect b) {
    return a.x * b.y - b.x * a.y;
}