#include<algorithm>
#define DIM 1000001
using namespace std;
int a[31];
char s[DIM];
void solve(){
    int i,n,ok,prev,next;
    gets(s);
    n=strlen(s);
    for(i=0; i<n; ++i)
        ++a[s[i]-'a'];
    for(ok=1,prev=-1; ok; ){
        for(i=0; i<26; ++i)
            if(a[i]&&i!=prev){
                printf("%c",i+'a');
                --a[i];
                prev=i;
                i=27;}
        if(i==26)
            ok=0;}}
int main(){
    freopen("ordine.in","r",stdin);
    freopen("ordine.out","w",stdout);
    solve();
    return 0;}