#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c;
	cin>>a;
	b=a%10;
	c=a%10/10;
	if(b>c){
		cout<<b;
	} 
	if(c>b){
		cout<<c;
	}
}
/**************************************************************
	Problem: 1622
	User: toughuatao1
	Language: C++
	Result: Wrong Answer
****************************************************************/