#include <iostream>
using namespace std;
int n, m, l, r;
const int maxn = 100010;
int a[maxn];
int s[maxn];
int main(){
cin >> n >> m;
for(int i = 1; i < n; i ++){
cin >> a[i];
s[i] = s[i - 1] + a[i];
}
while(m --){
cin >> l >> r;
cout << s[r] - s[l - 1] << endl;
}
return 0;
}