import java.util.Scanner;

public class Main{
  public static void main(String[] args){
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();
    int[] h = new int[n];
    for(int i = 0; i < n; i++){
      h[i] = scanner.nextInt();
    }
    
    boolean result = true;
    
    for(int i = n - 1; i > 0; i--){
      if(h[i-1] > h[i] + 1){
        result = false;
      }else if(h[i-1] > h[i]){
        h[i-1]--;
      }
    }

    System.out.println(result ? "Yes" : "No");
  }
}

/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