#include <bits/stdc++.h>
using namespace std;

void fast_io() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
}

int main() {
	fast_io();
	string s;
	cin >> s;
	for (char c : s) {
		if (c == 'a') {
			cout << c;
		}
	}
	cout << "a\n";
}