import java.io.PrintWriter;
import java.util.Scanner;

public class Main{

	public static void main(String[] args){
		//入力
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int h[] = new int[n];
		for(int i = 0; i < n; i++) h[i] = sc.nextInt();
		sc.close();

		//処理
		String ans = "Yes";
		for(int i = n-2; i >= 0; i--){
			if(h[i] > h[i+1]){
				h[i]--;
			}
		}
		for(int i = 0; i < n-1; i++){
			if(h[i] > h[i+1]) ans = "No";
		}
		
		//出力
		PrintWriter out = new PrintWriter(System.out);
		out.println(ans);
		out.flush();
	}
}
/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