import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = Integer.parseInt(sc.next());
		
		
		long save = Long.parseLong(sc.next());
		
		long s = 1;
		
		boolean judge = true;
		
		for (int i=1; i<N; i++) {
			s = Long.parseLong(sc.next());
			
			if (s - save > 0) {
				save = s -1;
			}
			
			if (s - save < 0) {
				judge = false;
				break;
			}
			
		}
		
		if (judge) {
			System.out.println("Yes");
		} else {
			System.out.println("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