import java.util.*;
public class Main{

 public static void main(String[] args)
 {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] list = new int[n];
        for(int i =0;i<n;i++){
          list[i] = sc.nextInt();
        }
        int first = list[0];
        int min = list[0] - 1;
        String judge = "Yes";
        for(int i=1;i<n;i++){
          if(min <= (list[i] - 1)){
              min = list[i] - 1;
          }else if(min == list[i]){
              min = list[i];
          }else{
              judge = "No";
          }
        }
        
        System.out.println(judge);
      
    }

}
/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