int main()
{
	vector<pair<char, int>> vec;
	map <char, int> m;
	char s;
	cin >> s;
	while (s != '.')
	{
		m[s] += 1;
		cin >> s;
	}
	for (auto itr = m.begin(); itr != m.end(); ++itr)
		vec.push_back(*itr);
	sort(vec.begin(), vec.end(), [=](pair<char, int>& a, pair<char, int>& b)
	{
		return a.second > b.second;
	}
	);
	for (auto x : vec)
	{
		cout << x.first;
	}
	return 0;
}