#include <iostream>
#include <fstream>
#include <string.h>

using namespace std;

ifstream f("ordine.in");
ofstream g("ordine.out");
char a[1000000];
int aux,ok;
long long i,j;
int main()
{
    f>>a;
    for(i=0;i<strlen(a);i++){
        for(j=i;j<strlen(a);j++){
            if(a[i]>a[j]){
                aux=a[i];
                a[i]=a[j];
                a[j]=aux;
            }
        }
    }
    ok=1;
    while(ok!=0){
        ok=0;
        for(i=0;i<strlen(a);i++){
            if(a[i]==a[i-1]){
                aux=a[i];
                a[i]=a[i+1];
                a[i+1]=aux;
                ok++;
            }
        }
    }
    for(i=0;i<strlen(a);i++) g<<a[i];
    return 0;
}