import java.io.BufferedReader;
import java.io.InputStreamReader;

import java.util.StringTokenizer;

public class Main {
	public static void main(String[] args) {
	
		try {
			BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));

			int n = Integer.parseInt(bf.readLine().trim());

			int p[] = new int[n+1];
			int i=1;
			
		    StringTokenizer st = new StringTokenizer(bf.readLine().trim());
		    while (st.hasMoreTokens()) {
		    	p[i] = Integer.parseInt(st.nextToken());
		    	i++;
		    }
		    
		    boolean ret = true;
		    for(i=n;i>1;i--) {
		    	if (p[i-1] <=p[i]) {
		    		continue;
		    	}else if (p[i-1]-1 == p[i]) {
		    		p[i-1]--;
		    	}else {
		    		ret = false;
		    		break;
		    	}
		    }
		    
		    if ( ret  ) {
		    	System.out.println("Yes");
		    }else{
		    	System.out.println("No");
		    }
		}catch(Exception e){
			e.printStackTrace();
		}
	
	}
}
/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