#include <bits/stdc++.h>
using namespace std;
using ll=long long;
int main(){
  ll N;
  cin>>N;
  vector<ll> S(N+1,0);
  for(int i=0;i<N;i++){
    string s;
    cin>>s;
    ll acount=0;
    for(int j=0;j<N;j++){
      if(s[j]=='a') acount++;
    }
    S[acount]++;
  }
  ll next=0;
  while(S[next]!=0) next++;
  string ans="";
  for(int i=0;i<next;i++) ans+="a";
  for(int i=0;i<N-next;i++) ans+="b";
  cout<<ans<<endl;
}