#include<cstdio>
#include<cstring>
#include<algorithm>

char s[1000000];
int F[255];

int main(){
	
	freopen("ordine.in","r",stdin);
	freopen("ordine.out","w",stdout);
	
	gets(s);
	
	int n = (int)strlen(s);
	
	for(int i=0;i<n;i++)
		F[(int)s[i]]++;
	
	for(int j='a';j<='z';j++)
		if(F[j]){
			F[j]--;
			s[0] = j;
			break;
		}
	
	for(int i=1;i<n;i++)
		for(int j='a';j<='z';j++)
			if(F[j] && s[i-1]!=j){
				s[i] = j;
				F[j]--;
				break;
			}
	
	puts(s);
	
	return 0;
	
}