A. New Year Transportation

http://codeforces.com/contest/500/problem/A

import java.util.Scanner;

public class Main {
    static final int MAX = Integer.MAX_VALUE;

    public static void main(String[] args) {
        Scanner io = new Scanner(System.in);
        int n = io.nextInt(), t = io.nextInt();
        int[] a = new int[n + 1];
        for (int i = 1; i <= n-1; i++) a[i] = io.nextInt();
        int x=1;
        while (x<t){
            x+=a[x];
            if (x==t) { System.out.println("YES");return; }
        }
        System.out.println("NO");
    }


}