import java.util.*;

class Main {
    public static void main (String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] arr = new int[n];

        for (int i = n-1; i >= 0; i--) {
            arr[i] = sc.nextInt();
        }

        String answer = "Yes";
        for (int i = 1; i < n; i++) {
            int diff = arr[i] - arr[i-1];
            if (diff > 1) {
                answer = "No";
                break;
            } else if (diff == 1) {
                arr[i]--;
            }
        }
        System.out.println(answer);
    }
}
/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