#include<bits/stdc++.h>
#include<iostream>
using namespace std;
 
vector<int> sor(const vector<int>& nums){
    int n=nums.size();
    vector <int> prefix(n+1,0);
    for(int i=0;i<n;i++){
        prefix[i] =  prefix[i-1]+nums[i];
    }
    return prefix;
 
}
 
int op(vector<int>& prefix,int l, int r){
    return prefix[r]-prefix[l-1];
}
 
int main(){
    vector<int> a={0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    vector<int> prefix=sor(a);
 
    int l=3,r=7;
    cout<<op(prefix,l,r);
 
 
}

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