package yukicoder150508;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		String[] s = new String[n];
		int len = 0;
		for (int i = 0; i < n; i++) {
			s[i] = sc.next();
			len += s[i].length();
		}

		StringBuffer ret = new StringBuffer();
		for (int i = 0; i < len; i++) {
			String min = "";
			int mini = -1;
			for (int j = 0; j < n; j++) {
				int sh = Math.min(min.length(), s[j].length());
				int comp = min.substring(0, sh).compareTo(s[j].substring(0, sh));
				if (comp == 0) {
					if (min.length() < s[j].length()) {
						min = s[j];
						mini = j;
					}
				} else if (comp > 0){
					min = s[j];
					mini = j;
				}
			}
			ret.append(min.charAt(0));
			s[mini] = s[mini].substring(1);
		}
		
		System.out.println(ret);

		sc.close();
	}
}