#include<stdio.h>
#include<string.h>

#define dim 29
char c;
int a[29];
int n,i,k,last=300;
void read()
{
 
while(scanf("%c",&c)!=EOF)
if(c-'a'>=0)
 a[c-'a']++,n++;
    //  printf("%d ",c-'a');
     
 }
void solve()
{
    for(i=1;i<=n;i++)
    {
     for(k=0;k<=26;k++)
     if(a[k] && k!=last)
     printf("%c",k+'a'),a[k]--,last=k;
}}
 int main ()
{
 
     freopen("ordine.in","r",stdin);
     freopen("ordine.out","w",stdout);
     read();
     solve();
     return 0;
}