#include <stdio.h>
int main()
{
	int max;
	int num;
	int rem;
	scanf ("%d", &num);
	max = num % 10;
	while (num > 0)
	{
		rem = num % 10;
		if (rem > max)
		{
			max = rem;
		}
		num = num / 10;
	}
	printf ("%d\n", max);
	return 0;
}