#include <fstream>
using namespace std;

char s[1<<20];
int v[1<<5];

ifstream in("ordine.in");
ofstream out("ordine.out");

int main()
{
	int n,i,j,x=0;
	in>>s;
	for (i=0;s[i];i++)
		v[s[i]-'a']++;
	n=i;
	while(!v[x]) x++;
	s[0]=x+'a';v[x]--;
	for (i=1;i<n;i++)
		for (j=0;j<26;j++)
			if (v[j] && x!=j)
			{
				v[j]--;
				s[i]=j+'a';
				x=j;
				break;
			}
	out<<s<<"\n";
	return 0;
}