#include<iostream>
#include<string>
#include<queue>
#include<functional>
using namespace std;
int main(void){
	int N;cin >> N;
	priority_queue<string, vector<string>, greater<string>> que;

	string s;
	for (int i = 0; i < N; i++){
		cin >> s;
		s += '{';
		que.push(s);
	}

	s = "";
	while (que.empty()==false){
		auto t = que.top(); que.pop();
		auto p = t[0];
		if (p == '{')break;
		s += p;
		que.push(t.substr(1, t.size() - 1));
	}
	cout << s << endl;
	return(0);
}