#include<iostream.h>
#include<stdio.h>
using namespace std;
int v[28];
int a[1000001];
int main()
{
	char c;
	int i,n=0,s=1,j,afis,ok,manevra;
	
	FILE *f=fopen("ordine.in","r"), *g=fopen("ordine.out","w");
	while(!feof(f))
		{fscanf(f,"%c",&c);
	    v[(int)c-96]++;n++;} n=n-2;
		//ok=0;
		while(s<=n)
		       {ok=1;
			for(j=1;j<=26;j++)
			 if(s!=n+1)
			 {
			 //if(ok==0)
			   if(v[j]==((n-s+1)/2+1))
				{manevra=j;ok=1;break;}
				   /*{a[s]=v[j];s++;v[j]--;ok=1;break;}*/
			else if( (v[j]!=0) && ok && j!=manevra)
				{manevra=j;ok=0;}
					/*{a[s]=j;s++;v[j]--;ok=0;}*/
			 }
			 a[s]=manevra;s++;v[manevra]--;
			 }
			 /*else {i=27;j=27;}*/
	s--;
	for(i=1;i<=s;i++)
		{afis=a[i]+96;
    fprintf(g,"%c",(char)afis);	}
	
	

fprintf(g,"\n");
fclose(f);
fclose(g);

return 0;
}