binary indexed tree 구현

void update(int x, int value) {
    while (x <= n) {
        tree[x] += value;
        x += -x&x;
    }
}

int sum_from_1_to(int x) {
    int s(0);
    while (x) {
        s += tree[x];
        x &= x - 1;
    }
    return s;
}