int query(int idx){
       int sum=0;
       while(idx>0){
             sum+=tree[idx];
             idx -= idx & (-idx);
       }
       return sum;
}

void update(int idx, int x, int n) //n is the size of the array, x is the number to add
{
       while(idx<=n)
       {
             tree[idx]+=x;
             idx += idx & (-idx);
       }
}