#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5;
char s[N];
vector<int>solve(vector<int>S){
	int n=S.size()-1,t=0;
	if(S[0]==S[n])return S;
	while(S[t]==S[0])++t;
	int p1=t-1,p2=t-1;
	vector<vector<int> >a(t);
	for(int i=0;i<t;++i)a[i].push_back(S[i]);
	for(int i=n;i>=t;--i){
		if(i!=n&&S[i]!=S[i+1])p2=p1;
		a[p1].push_back(S[i]);
		--p1;
		if(p1<0)p1=p2;
	}
	vector<int>T(t);
	for(int i=0,j=0;i<t;++i){
		if(i&&a[i]!=a[i-1])j=i;
		T[i]=j;
	}
	vector<int>o=solve(T),ans;
	for(int i=0;i<t;++i)
		for(auto v:a[o[i]])ans.push_back(v);
	return ans;
}
int main(){
	scanf("%s",s+1);
	int n=strlen(s+1);
	vector<int>S,ans;
	for(int i=1;i<=n;++i)S.push_back(s[i]-'a');
	sort(S.begin(),S.end());
	ans=solve(S);
	for(int i=0;i<n;++i)putchar(ans[i]+'a');
	return 0;
}