#include<bits/stdc++.h>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
using ll = long long;
int n;
vector<string> s;

void solve(){
	string t;
	for(int i = 0;i<n;i++){
		s[i].push_back('z'+1);
	}
	for(int i = 0;s.size();i++){
		sort(s.begin(),s.end());
		t.push_back(s[0][0]);
		s[0].erase(s[0].begin());
		if(s[0].size()==1){
			s.erase(s.begin());
		}
	}
	cout<<t<<endl;
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cin >> n;
	s = vector<string>(n);
	for(auto &i:s)cin >> i;
	solve();
}