#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#include <queue>

using namespace std;

const char CHAR = 'z' + 1;

int main() {
	int n;
	string input;

	cin >> n;

	priority_queue<string, vector<string>, greater<string> > que;
	for (int i = 0; i < n; i++) {
		cin >> input;
		input.append(string(50, CHAR));
		que.push(input);
	}

	string ans;
	string str;
	while(!que.empty()) {
		str = que.top();
		que.pop();
		ans += str[0];
		str = str.substr(1);
		if (str[0] != CHAR) {
			que.push(str);
		}
	}
	cout << ans << endl;
	return 0;
}