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