#include <iostream>
#include <fstream>
#include <cstring>
#include <list>
 
using namespace std;
 
 
int L[30];
 
string a;
string b;
 
int sum;
int last;
 
int valid()
{
    for ( int i = 1; i <= 26; ++i )
            if ( L[i] > 0 && i != last )
            {
                if ( L[i] >= sum/2 + 1 )
                        return i;
            }
 
    return -1;
}
 
int main()
{
    ifstream f("ordine.in");
    ofstream g("ordine.out");
 
    f >> a;
 
    sum = a.length();
 
    for ( int i = 0; i < sum; ++i )
            L[ a[i] - 96 ]++;
 
    while( sum > 0 )
    {
        int elem = valid();
 
        if ( elem == -1 )
        {
            for ( int i = 1; i <= 26; ++i )
                    if ( L[i] > 0 && i != last )
                    {
                        b.push_back( char( 96 + i ) );
                        L[i]--;
                        sum--;
                        last = i;
 
                        break;
                    }
        }
        else
        {
            b.push_back( char( 96 + elem ) );
            L[elem]--;
            sum--;
 
            last = elem;
        }
    }
 
    g << b << "\n";
 
    f.close();
    g.close();
 
    return 0;
}