
import java.util.*;
public class Main {
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
String N = scan.next();
char max = '0';
for(int i = 0; i < N.length(); i++)
{
if(N.charAt(i) > max)
max = N.charAt(i);
}
System.out.println(max);
}
}


