import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        if(n == 1){
            System.out.println(true);
            return;
        }
        int[] a = new int[n];
        for(int i = 0; i < n; i++)a[i] = in.nextInt();
        in.close();
        int cover = 0;
        boolean flag = false;
	  // 用一个覆盖范围来判断,在覆盖范围内的都是可以跳到的
        for(int i = 0; i <= cover; i++){
            cover = Math.max(cover, i+a[i]);
            if(cover >= n-1){
                flag = true;
                break;
            }
        }
        System.out.println(flag);
    }
}