#include<iostream>
#include<bits/stdc++.h>
using namespace std;
const int N=110;
int d[N];
int main()
{
    int n;
    cin>>n;
    for(int i=1;i<=n-1;i++)cin>>d[i];
    int a,b;
    cin>>a>>b;
    int res=0;//答案
    for(int i=a;i<b;i++)res+=d[i];
    cout<<res;
}