#include<stdio.h>
#define dim 27
int a[dim];
void solve()
{
     char x,nr=0,i;
    // printf("%d",'z'-'a');
     while(scanf("%c",&x)!=EOF)
     {
                               if(x-'a'<0 || x-'a'>26)
                               break;
                               a[x-'a']++;
                               nr++;
                               }
                               int in=100,n=nr,k;
     for(i=0;i<=n;i++)
     {
                      for(k=0;k<=26;k++)
                      {
                                        if(k!=in && a[k]!=0)
                                        {
                                                 printf("%c",k+'a');
                                                 a[k]--;
                                                 in=k+'a';
                                                 }}}
}
int main ()
{
    freopen("ordine.in","r",stdin);
    freopen("ordine.out","w",stdout);
    solve();
    printf("\n");
    return 0;
}