#include<fstream>
#include<cstring>
using namespace std;
int n;
char c;
int uz[27];
int main()
{
	ifstream fin("ordine.in");
	ofstream fout("ordine.out");
	while(fin>>c)
		uz[c-97]++,n++;
	c='0';
	while(n)
		for(int i=0;i<=26;++i)
			if( c != char(i+97) && uz[i])
			{
				c=char(i+97);
				fout<<char(i+97);
				n--;
				uz[i]--;
				break;
			}
}