#include <iostream>
#include <fstream>
#include <string.h>
#include <algorithm>
#define MAX 1000000
using namespace std;

int main()
{ ifstream in("ordine.in");
ofstream out("ordine.out");
 int i;
 char s[MAX];
 in>>s;

sort(s,s+strlen(s));
out<<s[0];
int k;
for(i=0;i<strlen(s);i++)
{

  k=i;
 if(s[i]==s[i+1])
{while(s[i]==s[k])
k++;
swap(s[i+1],s[k]); }



}
     cout<<s; return 0;
}