cpp/container/deque

struct vec{

   ll x, y;

   vec() {}
   vec(ll x, ll y): x(x), y(y) {}
   vec(ll x, ll y, ll x1, ll y1): x(x1 - x), y(y1 - y) {}

   ll operator* (vec &a) {
       return x * a.x + y * a.y;
   }
   ll operator/ (vec &a) {
       return x * a.y - y * a.x;
   }
   vec operator- (vec &a) {
       return { x - a.x, y - a.y };
   }

   friend istream& operator>> (istream& is, vec &a) {
       is >> a.x >> a.y;
       return is;
   }
   friend ostream& operator<< (ostream& os, vec &a) {
       os << a.x << " " << a.y;
       return os;
   }

};