Untitled

import java.util.Scanner;

public class P1 {
	public static boolean Sol(int n) {
		int tmp = n % 10;
		n = n / 10;

		while (n != 0) {
			if (tmp > n % 10)
				return false;
			n /= 10;
		}

		return true;
	}

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

		int n = sc.nextInt();

//		System.out.println(Sol(n));
//		Sol(n);
		if (Sol(n)) {
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}
	}
}