#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)

using namespace std;
using LL = long long;
using P = pair<int,int>;
using vv = vector<vector<int>>;
const int INF = (int)1e9;
const LL LINF = (LL)1e18;

int main(){
	string S;
	cin >> S;
	int num = 0;
	rep(i,S.size()) if(S[i] == 'a') num++;
	string ans;
	rep(i,num+1) ans.push_back('a');
	cout << ans << endl;

	return 0;
}