import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		String ans = "Yes";

		for (int i = n - 1; i > 0; i--) {
			if (n == 1) {
				break;
			}
			else if (h[i] - h[i-1] > -1) {
				continue;

			} else if (h[i] - h[i-1] == -1 ) {
				h[i-1]--;
				continue;

			} else {
				ans = "No";
				break;
			}
		}

		System.out.println(ans);
		sc.close();
	}
}
/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