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);
}
}