package asda;
import java.util.Scanner;
public class Main
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
String s = scan.nextLine();
int l = s.length();
int max = 0;
for(int i=0; i < l; ++i)
if(s.charAt(i)>max)
max = s.charAt(i);
max-=48;
System.out.println(max);
}
}