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();
    }
    
    String s = "Yes";
    int pre = -1;
    for (int i = 0; i < n; i++) {
      if (pre <= h[i] - 1) {
        pre = h[i] - 1;
      } else if (pre <= h[i]) {
        pre = h[i];
      } else {
        s = "No";
        break;
      }
    }

    System.out.println(s);
  }
}

/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