#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, dp[105], a, b;
  memset(dp, 0, sizeof dp);
  cin >> n;
  for (int i = 1; i < n; ++i) {
    cin >> dp[i];
    dp[i] += dp[i - 1];
  }
  cin >> a >> b;
  cout << dp[b - 1] - dp[a - 1];
  return 0;
}
