import java.util.Scanner;
public class Main{
 
	public static void main(String[] args) {
      int max = 0;
      int a = 0;
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
      for(int i = 0;i<=n;i++){
        if(i==n){
          System.out.println("Yes");
          break;
        }
        
        a=sc.nextInt();
        if(max<a)
          max=a-1;
        else if(max==a)
          max=a;
        else{
          System.out.println("No");
          break;
        }
      }
 
      
      
 
 
 
		
		
	}
 
}
/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