import java.util.*;
import static java.lang.Math.*;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		// 入力
		int n = sc.nextInt();
		int[] h = new int[n];
		
		String result = "Yes";
		
		for(int i = 0; i < n; i++){
		    h[i] = sc.nextInt();
		    if(i > 0 && h[i - 1] < h[i]){
                h[i]--;		        
		    }else if(i > 0 && h[i - 1] > h[i]){
		        result = "No";
		    }
		}
		
		// 計算

		// 出力
        System.out.println(result);
		
	}
}

/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