
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] nums = new int[N];

		for (int i = 0; i < N; i++) {
			nums[i] = sc.nextInt();
		}
		if (nums.length == 1) {
			System.out.println("Yes");
		}else {
			int lim = nums[0];
			for (int i = 1; i < N; i++) {
				if (nums[i] < lim) {
					System.out.println("No");
					break;
				}
				if (nums[i-1] - nums[i] < -1) {
					lim = nums[i]-1;

				}
				if (i == N-1) {
					System.out.println("Yes");
					break;
				}

			}
		}
	}
}



/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