import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		long[] h = new long[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextLong();
		}
		sc.close();
		for (int i = 0; i < h.length - 1; i++) {
			if (h[i] > h[i + 1])
				h[i]--;
			else if (i != 0 && (h[i] - h[i - 1]) >= 1)
				h[i]--;
		}
		for (int i = 0; i < h.length - 1; i++) {
			if (h[i] > h[i + 1]) {
				System.out.println("No");
				return;
			}
		}
		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