#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
using namespace std;

int main()
{
	int n;
	vector<string> s;
	string temp, ans = "";
	cin >> n;

	while (n--) {
		cin >> temp;
		temp.push_back('z' + 1);
		s.push_back(temp);
	}
	while (s.size()) {
		sort(s.begin(), s.end());
		ans.push_back(s[0].front());
		s[0].erase(s[0].begin());
		if (s[0].size() == 1)s.erase(s.begin());
	}
	cout << ans << endl;
	return 0;
}