#include <bits/stdc++.h> using namespace std; char s[1005]; int main() { cin>>s; char max='0'; double len=strlen(s); for(int i=0;i<len;i++){ if(s[i]>='0' && s[i]<='9'){ if(s[i]>max){ max = s[i]; } } } cout<<max<<endl; return 0; }