#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,g,s,b,q;
    cin>>n;
    g=n%10;
    s=n/10%10;
    b=n/100%10;
    q=n/1000;
    int max=g;
    if (max<s){
    	max=s;
	}
	if (max<b){
    	max=b;
	}
	if (max<q){
    	max=q;
	}
	cout<<max<<endl;
}
/**************************************************************
	Problem: 1718
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:24 ms
	Memory:2072 kb
****************************************************************/