import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Main main = new Main();
        main.exec();
    }

    private void exec() {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();
        scanner.nextLine();

        List<String> words = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            words.add(scanner.nextLine());
        }
        Collections.sort(words);
        StringBuilder result = new StringBuilder();
        for (String word : words) {
            result.append(word );
        }
        System.out.println(result);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz