import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		int n = stdIn.nextInt();
		int[]h = new int[n];
		for(int i = 0; i < n; i++) {
			h[i] = stdIn.nextInt();
		}
		if(n==1) {
			System.out.println("Yes");
			System.exit(0);
		}
		int max = 0;
		
		for(int i = 0; i < n-1; i++) {
			if(max == h[i]) {
				if(h[i] > h[i+1]) {
					System.out.println("No");
					System.exit(0);
				}
			}
			if(h[i]-1 > h[i+1]) {
				System.out.println("No");
				System.exit(0);
			}
			h[i]--;
			max = Math.max(h[i], max);
		}
		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