#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("ordine.in");
ofstream cout("ordine.out");
int v[1000005];
int main()
{
    int n=0,i,j;
    while(1)
    {
        char ch;
        ch=cin.get();
        if(ch=='\n')
            break;
        v[++n]=int{ch};
    }
    sort(v+1,v+n+1);
    bool ok=0;
    while(!ok)
    {
        ok=1;
        for(i=n-1;i>1;i--)
            if(v[i]==v[i-1])
            {
                swap(v[i],v[i+1]);
                ok=0;
                break;
            }
    }
    for(i=1;i<=n;i++)
        cout<<char{v[i]};
    cin.close();
    cout.close();
    return 0;
}