#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define dim 16000
int a[27],n,i,k;
char x,an;
void solve()
{
     n=1;
     scanf("%c",&x);
     while(isalpha(x)!=0)
     {                  
                  ++a[x-'a'];
                  n++;
                  scanf("%c",&x);
                  
}
             /*     for(i=0;i<=26;i++)
                  if(a[i]>n/2+1)
                  {printf("%c",(char)i+'a');
                  a[i]--;
                  an=a[i];
                  }*/
for(i=1;i<=n;i++)
for(k=0;k<=26;k++)
{
                  if(an!=(char)(k+'a') && a[k]!=0)
                  {
                                     a[k]--;
                                     an=(char)(k+'a');
                                     printf("%c",an);
                                     break;
}}
}
int main ()
{
    freopen("ordine.in","r",stdin);
    freopen("ordine.out","w",stdout);
    solve();
    return 0;
}