#include<iostream>
#include<cstdio>
#include<vector>
#include<algorithm>
#define N 1000000
using namespace std;
int read()
{
	char c=0;
	int sum=0;
	while (c<'0'||c>'9') c=getchar();
	while ('0'<=c&&c<='9') sum=sum*10+c-'0',c=getchar();
	return sum;
}
int n,cnt[26];
char c[N+1];
string s,t[N+1];
vector<char>p[N+1];
int main()
{
	cin>>s,n=s.length();
	for (int i=1;i<=n;++i) t[i]=t[i]+s[i-1];
	for (int i=n;i>=2;--i) sort(t+1,t+i+1),t[1]=t[1]+t[i];
	for (int i=0;i<t[1].length();++i) printf("%c",t[1][i]);
	puts("");
	return 0;
}