#include<stdio.h>
#include<string.h>
#define DIM 1000001
char s[DIM],aux;
int n;
int main ()
{
    freopen("ordine.in","r",stdin);
    freopen("ordine.out","w",stdout);
    int i,j;
    gets (s);
    n=strlen(s);
    for(i=0;i<n;++i)
        for(j=i+1;j<n;++j)
            if((s[i]>s[j] && s[i-1]!=s[j]) || s[i-1]==s[i])
            {
                aux=s[i];
                s[i]=s[j];
                s[j]=aux;
            }
    printf("%s",s);       
    return 0;
}