#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 1e6 + 10, INF = 0x3f3f3f3f, MOD = 1E9 + 7;
int n, m, a[N], s[N];

int main(int argc, char* argv[]) {
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        cin >> a[i], s[i] = s[i - 1] + a[i];
    int l,r;
    while (m--) {
        cin >> l >> r;
        cout << s[r] - s[l - 1] << endl;
    }
    return 0;
}

$$\begin{array}{c} &一维前缀和:S_k = \sum_{i = 1}^k{a_i};\\ &\sum_{i = l}^{r}{a_i} = S_{r}-S_{l-1}\\ \\ &二维前缀和:S_{i,j} = \sum_{i = 1}^n \sum_{j = 1}^n a_{i,j}; \\ &\sum_{i = x_1}^{x_2} \sum_{j = y_1}^{y_2} {a_{i,j}} = S_{x_2,y_2}-S_{x_1-1,y_2}-S_{x_2,y_1-1}+S_{x_1-1,y_1-1} \\ \\ &一维差分：D_i = a_i-a_{i-1}\\ &a_k = \sum_{i = 1}^k{D_i}\\ \\ &二维差分：D_{i,j} = a_{i,j}-a_{i-1,j}-a_{i,j-1}+a_{i-1,j-1}\\ &D[x_1][y_1] + = c;\\ &D[x_1][y_2+1] - = c;\\ &D[x_2+1][y_1] - = c;\\ &D[x_2+1][y_2+1] + = c;\\ \end{array} $$