#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    int x;
    string s;
    cin >> s;
    sort (s.begin(),s.end());
    for (int i=1; i<s.size(); i++)
    {
        if (s[i]!=s[i-1])
        continue;
        for (x=i+1; x<s.size(); x++)
        {
            if(s[x]!=s[i])
            break;
        }
        swap(s[x],s[i]);
    }
    cout << s;
    return 0;
}