#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, t;
  cin >> n >> t;
  int f = 0;
  int x;
  int sum = 1;
  for (int i = 1; i < n; i++) {
    cin >> x;
    if (i == sum) sum += x;
    if (sum == t) f = 1;
  }
  if (f == 1)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
