#include <iostream>
#include <map>
using namespace std;
signed main() {
pair<char, int> res = {' ', 0};
map<char,int> m;
string s;
getline(cin, s);
for(auto &i : s){
i = tolower(i);
if(i < 'a' || i > 'z') continue;
m[i]++;
if(m[i] > res.second)
res = {i,m[i]};
}
cout << res.first;
}
