#include <bits/stdc++.h>
using namespace std;
bool comp(const pair<char, int> & a, const pair<char, int> & b) {
return a.second < b.second; }
int main()
{
string n, vocale = "aeiouAEIOU";
map<char, int> aparitii;
getline(cin, n);
for(int i = 0; i < n.size(); i++)
if(vocale.find(n[i]) != string::npos)
aparitii[tolower(n[i])]++;
cout << max_element(aparitii.begin(), aparitii.end(), comp) -> first << '\n';
return 0;
}