import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		ArrayList<LinkedList<Character>> chars = new ArrayList<LinkedList<Character>>();
		for(int i = 0; i < N; i++){
			final char[] input = sc.next().toCharArray();
			
			LinkedList<Character> list = new LinkedList<Character>();
			for(final char c : input){
				list.add(c);
			}
			
			chars.add(list);
		}
		
		StringBuilder sb = new StringBuilder();
		while(true){
			char min = '\0';
			int min_pos = -1;
			
			for(int i = 0; i < N; i++){
				final LinkedList<Character> list = chars.get(i);
				
				if(list.isEmpty()){ continue; }
				if(min_pos < 0 || list.peek() < min){
					min = list.peek();
					min_pos = i;
				}else if(list.peek() == min){
					final int list_prev = list.size() == 1 ? Integer.MAX_VALUE : list.get(1);
					final int min_pos_prev = chars.get(min_pos).size() == 1 ? Integer.MAX_VALUE : chars.get(min_pos).get(1);
					
					if(list_prev < min_pos_prev){
						min_pos = i;
					}
				}
			}
			
			if(min_pos < 0){ break; }
			sb.append(chars.get(min_pos).poll());
		}
		
		System.out.println(sb.toString());
		
		
	}

}