import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		try(Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			
			int[] cells = new int[n];

			for(int i = 0 ; i < n ; i++ ) {
				cells[i] = sc.nextInt();
			}
			
			int rightHeight = cells[n-1];
			for(int i = 1 ; i < n ; i++ ) {
				//right to left
				int current = cells[n-i-1];
				if ( current == rightHeight ||  current - 1 == rightHeight ) {
					//ok
				}
				else if ( current < rightHeight ) {
					rightHeight = current;
				}
				else {
					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