
import java.util.Scanner;
public class Main
{
public static void main(String[] args)
{
Scanner x = new Scanner(System.in);//构造一个SCANNER对象,其传入参数为SYSTEM.IN
int n = x.nextInt();//读取一个INT数值
int[] data = new int[20];
int i = 0, max = 0;
while (n != 0)
{
data[i++] = n % 10;
n = n / 10;
}
for ( int j =0; j < i; j++)
{
if (data[j] > max)
max = data[j];
}
System.out.println(max);
}
}


