#include <fstream>
#include <vector>

using namespace std ;

ifstream f ("ordine.in") ;
ofstream g ("ordine.out") ;

vector < int > v ( 26 , 0 ) ;
int j = -1 , cnt ;

int main ()
{
    char c ;
    while ( f >> c )    v [ c - 'a' ] ++ , cnt ++ ;
    int p = 0 ;
    while ( cnt -- )
    {
        for ( int i = 0 ; i < 26 ; ++ i )   if ( v [ i ] && i != j )  { g << char ( i + 'a' ) , v [ i ] -- , j = i ; break ; }
    }


    return 0 ;
}