import java.util.Scanner;

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

        int n = sc.nextInt();

        if (n == 1) {
            System.out.println("Yes");
            return;
        }

        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
            list[i] = sc.nextInt();
        }

        for (int i = 1; i < n; i++) {
            if (list[i-1] == list[i]) continue;
            else if (list[i-1] <= list[i]-1) list[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