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template <typename T>
struct Fenwick {
    size_t n;
    vector<T> a;

    Fenwick(int n_ = 0) {
        init(n_);
    }

    void init(int n_) {
        n = n_;
        a.assign(n, T{});
    }

    void add(int x, const T &v) {
        for (int i = x + 1; i <= n; i += i & -i) {
            a[i - 1] = a[i - 1] + v;
        }
    }

    T sum(int x) {
        T ans{};
        for (int i = x; i > 0; i -= i & -i) {
            ans = ans + a[i - 1];
        }
        return ans;
    }

    T rangeSum(int l, int r) {
        return sum(r) - sum(l);
    }

    int select(const T &k) {
        int x = 0;
        T cur{};
        for (int i = 1 << bit_width(n); i; i /= 2) {
            if (x + i <= n and cur + a[x + i - 1] <= k) {
                x += i;
                cur = cur + a[x - 1];
            }
        }
        return x;
    }
};