#include <iostream>
using namespace std;
int maxim;
bool numarPalindrom(int nr) {
int nri,nrf=0;
nri=nr;
while(nr) {
int c=nr%10;
nrf=nrf*10+c;
nr=nr/10;
if(c>maxim) maxim=c;
}
if(nri==nrf)
return true;
return false;
}
int main()
{
int n;
cin>>n;
if(numarPalindrom(n)) cout<<(n%10);
else cout<<maxim;
return 0;
}
