#include <bits/stdc++.h>

using namespace std;

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	string res,s;
	int n;
	priority_queue <string,vector<string>,greater<string>> pque;

	cin >> n;

	for (int i = 0; i < n; i++)
	{
		cin >> s;
		s += '\xff';
		pque.push(s);
	}

	while (!pque.empty())
	{
		string now = pque.top();
		pque.pop();

		res += now[0];
		if (now.substr(1).length() > 0)
		{
			pque.push(now.substr(1));
		}
	}

	cout << res << '\n';

	return 0;
}