import java.util.Scanner;
public class Main{

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		long max = 0;
		
		long[]h = new long[n];
		
		for(int i = 0; i < n; i++) {
			h[i] = stdIn.nextLong();
		}
		
		boolean flag = false;
		
		for(int i = 0; i < n-1; i++) {
			max = Math.max(max, h[i]);
			
			if(h[i] > h[i+1]) {
				if(h[i]-1 > h[i+1] || h[i]-1 != max - 1) {
					flag = true;
				}
			}
		}
		
		if(flag) {
			System.out.println("No");
		}else {
			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