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

int main()
{
	string S;
	cin >> S;

	int N = S.size();
	int n = 0;
	for( int i = 0; i < N; i++ ) if( S[i] == 'a' ) n++;
	string ans = string( n + 1, 'a' );

	cout << ans << endl;
}