import java.util.Scanner;

public class Main {
	public static void main(String[]args) {
		try(Scanner scan = new Scanner(System.in)){
			Scanner sc = new Scanner(System.in);
			int N = sc.nextInt();
			int[] X = new int[N];
			for(int i = 0; i < N; i++) {
				X[i] = sc.nextInt();
			}
			boolean flag = true;
			for(int i = N - 2 ; i >= 0; i--) {
				if(X[i] > X[i + 1]) {
					if(X[i] - X[i + 1] == 1)X[i]--;
					else{
						flag = false;
						break;
					}
				}
			}
	 
			System.out.println((flag)?"Yes":"No");
	 
		}
			
			
			
	}
}


/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