#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int ar[n], a, b, sum = 0;
  for (int i = 0; i < n - 1; i++) cin >> ar[i];
  cin >> a >> b;
  a--;
  b--;
  for (int i = a; i < b; i++) sum += ar[i];
  cout << sum << endl;
  return 0;
}
