префиксы

#include <iostream>
#include <tuple>
#include <random>


using std::pair;
using std::cin;
using std::cout;
using std::vector;
using int64 = int64_t;
using std::max;
using std::min;

int main() {
    std::ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m;
    cin >> n >> m;
    vector<int64> val(n);
    for (size_t i = 0; i < n; ++i) {
        cin >> val[i];
    }
    vector<int64> pref(n);
    pref[0] = val[0];
    for (int i = 1; i < pref.size(); ++i){
        pref[i] = val[i] + pref[i-1];
    }
    for (size_t i = 0; i < m; ++i){
        int l, r;
        cin >> l >> r, --l, --r;
        if (l == 0){
            cout << pref[r] << '\n';
        } else {
            cout << pref[r] - pref[l-1] << '\n';
        }
    }
    return 0;
}