BIT fen0(n);
  BIT fen1((n+K-1)/K);

  void insert(int x0, int x1, int factor) {
    while (x0%K != 0 and x0 < x1) fen0.insert(x0++, factor);
    while (x1%K != 0 and x0 < x1) fen0.insert(--x1, factor);

    fen0.insert(x0, +factor*(1-x0));
    fen0.insert(x1, -factor*(1-x1));

    fen1.insert(x0/K, +factor);
    fen1.insert(x1/K, -factor);
  }

  int get(int x){
    return fen0.get(x) + fen1.get(x/K)*x;
  }