#include "bits/stdc++.h"

#define int long long

using namespace std;
using ll = long long;
using P = pair<ll, ll>;
const ll INF = (1LL << 61);
ll mod = 1000000007;

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	string S; cin >> S;
	int cnt = 0;
	int N = S.size();
	for (int i = 0; i < N; i++) {
		if (S[i] == 'a')cnt++;
	}
	cout << 'a';
	for (int i = 0; i < cnt; i++)cout << 'a';
	cout << endl;
	return 0;
}