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