#include <fstream>
#include <algorithm>
#include <cstring>
using namespace std;
ifstream cin("ordine.in");
ofstream cout("ordine.out");
char s[1000010],ch;
int N,fr[30],nr,ant,p;
int main()
{
    cin.getline(s,1000001);
    N=strlen(s);
    for(int i=0;i<N;i++)
        fr[s[i]-'a']++;
    ant=-1;
    for(int l=0;l<N;l++)
    {
        p=-1;
        for(int i=0;i<26;i++)
            if(((fr[i]>0&&p<0)||(fr[i]>=(N-l)/2+1&&ant!=i))&&i!=ant)
                p=i;
        cout<<(char)(p+'a');
        ant=p;fr[p]--;
    }
    cout<<'\n';
    return 0;
}