#include<iostream>
#include<cmath>
#include<string>
#include<vector>
#include<algorithm>
#include<cstdio>
using namespace std;
main(){
       string s[1001],s1,s2;
	   long n,i;
	 while(cin>>n){
	 			   if (n==0) break;
	 	 for (i=0;i<n;i++){
		 	 cin>>s[i];
	 	 }		   
	 	 sort(s,s+n);
	 	 s1=s[n/2-1];
	 	 s2=s[n/2];
	 	 i=0;
	 	 while (i<s1.size()&&i<s2.size()){
		 	   if (s1[i]==s2[i]) cout<<char(s1[i]);
		 	   else {
			   		if (s1[i]<s2[i]) {
					   if (i==s1.size()-1) cout<<char(s1[i]); 				 
			   		   else cout<<char(s1[i]+1);
					   }
			   		if (s1[i]>s2[i]) {
					   	if (i==s2.size()-1) cout<<char(s2[i]); 				 
			   		   else cout<<char(s2[i]+1);			 
			   		}
			   		break;
		 	   }
		 	   i++;
	 	 }
	 	 cout<<'\n';
	 }  
}