#include<fstream>
#define dmax 1000004

using namespace std;
ifstream in("ordine.in");
ofstream out("ordine.out");

char x[dmax],s[dmax];
long int n;
int y[dmax];

int main()
{	int i,j,ok;
	in>>x;
	in.close();
	n=strlen(x);
	for(i=0;i<n;i++)
		y[x[i]-'a']++;
	for(i=0;i<n;i++)
	{	ok=1;
		for(j=0;j<27 && ok;j++)
			if(y[j] && j!= s[i-1]-'a')
			{	y[j]--;
				s[i]='a'+j;
				ok=0;
			}
	}		
	out<<s;	
	out.close();
	return 0;
}