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];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

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

		System.out.print(flag ? "Yes" : "No");
		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