import java.util.*;

public class Main {

  public static void main (String[] args) {

    Scanner sc = new Scanner(System.in);
    
    int N = sc.nextInt();
    
    int[] H = new int[N];

    for (int i = 0; i < N; i++) {
      H[i] = sc.nextInt();
    }

    sc.close();

    for (int i = N-2; 0 <= i; i--) {

      if (H[i] > H[i+1]) {
        if (H[i] - H[i+1] == 1) {
          H[i]--;
        } else {
          System.out.println("No");
          return;
        }
      }
    }

    System.out.println("Yes");
    
  }

}
/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