#include<bits/stdc++.h> using namespace std; int main() { string n; cin >> n; int s = n[0] == '-' ? 1 : 0; char m = '0'; for (int i = s; i < n.length(); i++) { if (n[i] >= '0' && n[i] <= '9') { m = max(m, n[i]); } } cout << m << endl; return 0; }