import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int sum = 0;
		ArrayList<Deque<Character>> deques = new ArrayList<>();
		for (int i = 0; i < N; i++) {
			deques.add(new ArrayDeque<Character>());
		}

		for (int i = 0; i < N; i++) {
			char[] string = sc.next().toCharArray();
			sum += string.length;
			for (int j = 0; j < string.length; j++) {
				deques.get(i).addLast(string[j]);
			}
		}
		sc.close();

		StringBuilder sb = new StringBuilder();
		while (sb.length() < sum) {
			int mini = 0;
			char minchar = 'z' + 1;
			for (int i = 0; i < deques.size(); i++) {
				if (deques.get(i).isEmpty()) {
					continue;
				}
				if (minchar > deques.get(i).peekFirst()) {
					mini = i;
					minchar = deques.get(i).peekFirst();
				}
			}
			sb.append(deques.get(mini).pollFirst());
		}
		System.out.println(sb.toString());

	}
}