import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		long a = sc.nextLong();
		long max = a;
		for (int i =0;i<N-1;i++) {
			long temp = sc.nextLong();
			if (temp<max) {
				System.out.println("No");
				return ;
			}
			if (temp >= a+1) {
				a = temp-1;
			} else if (a>=temp+2) {
				System.out.println("No");
				return ;
			}
			max = a;
		}
		System.out.println("Yes");
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz