#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
int n;
char s[1000005];
vector<int> work(vector<int> qwq){
	int c=0,l=(int)qwq.size();
	while(c<l&&qwq[c]==qwq[0])c++;
	if (c==l)return qwq;
	vector<vector<int>> awa(c);
	for (int i=0;i<c;i++)awa[i].push_back(qwq[i]);
	int p1=c-1,p2=c-1;
	for (int i=l-1;i>=c;i--){
		if (i==l-1||qwq[i]!=qwq[i+1])p2=p1;
		awa[p1].push_back(qwq[i]);
		p1--;
		if (p1<0)p1=p2;
	}
	vector<int> ovo(c);
	int t=0;
	for (int i=0;i<c;i++){
		if (i>0&&awa[i]!=awa[i-1])t=i;
		ovo[i]=t;
	}
	vector<int> ord=work(ovo),ans;
	for (int i=0;i<c;i++)
		for (int j=0;j<(int)awa[ord[i]].size();j++)
			ans.push_back(awa[ord[i]][j]);
	return ans;
}
int main(){
	scanf("%s",s+1);
	n=strlen(s+1);
	vector<int> qwq;
	for (int i=1;i<=n;i++)qwq.push_back(s[i]-'a');
	sort(qwq.begin(),qwq.end());
	vector<int> ans=work(qwq);
	for (int i=0;i<n;i++)putchar(ans[i]+'a');
	putchar('\n');
	return 0;
}