#include <iostream>
using namespace std;
const int MAXN = 105;
int dp[MAXN], obstacle[MAXN];
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> obstacle[i];
    dp[i] = n - 1;
  }
  dp[1] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= i + obstacle[i] && j <= n; j++) {
      dp[j] = min(dp[j], dp[i] + 1);
    }
  }
  cout << dp[n] << endl;
}