Untitled

import java.util.Scanner;

public class P1 {
	public static int Sol(int n) {
		int sumValue = 0;
		while (n != 0) {
			sumValue = Math.max(sumValue, n % 10);
			n /= 10;
		}

		return sumValue;
	}

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

		int n = sc.nextInt();

		System.out.println(Sol(n));
//		Sol(n);

	}
}