class FenwickTree
{
    int size;
    vector<int> a;
    vector<long long> t;

    long long get(int index) {
        long long result = 0;
        for (; index > 0; index -= index & -index) {
            result += t[index];
        }

        return result;
    }

    void update(int index, int delta) {
        for (; index < size; index += index & -index) {
            t[index] += delta;
        }
    }

    public:
        FenwickTree(vector<int> a)
        : a(a)
        , size(a.size() + 1)
        , t(size, 0)
        {
            for (int i = 0; i < a.size(); ++i) {
                update(i + 1, a[i]);
            }
        }

        void set(int index, int value) {
            int delta = value - a[index];
            a[index] = value;
            update(index + 1, delta);
        }

        long long get_segment(int start, int end) {
            return get(end + 1) - get(start);
        }
};