import collections
import itertools


class Deque(collections.deque):
    def __le__(self, other):
        for e1, e2 in itertools.zip_longest(
                #
                self, other, fillvalue='{'):
            if e1 == e2:
                continue
            elif e1 < e2:
                return True
            elif e1 > e2:
                return False
        return True

    def __lt__(self, other):
        return Deque.__le__(self, other) and not Deque.__eq__(self, other)


def main():
    str_deque = initialize()
    up_heap(str_deque)
    print(min_dict_order(str_deque))


def initialize():
    N = int(input())
    str_deque = Deque(Deque(input()) for i in range(N))
    return str_deque


def up_heap(str_deque: Deque):
    for index in range(len(str_deque) - 1, -1, -1):
        min_index = get_min_index(str_deque, index)
        if min_index != index:
            swap(str_deque, index, min_index)


def min_dict_order(str_deque: Deque):
    seq = ''
    while True:
        for e in str_deque:
            print(e)
        chr_deque = str_deque[0]
        seq += chr_deque.popleft()
        if not chr_deque:
            str_deque.popleft()
            try:
                str_deque.appendleft(str_deque.pop())
            except IndexError:
                break
        down_heap(str_deque)
    return seq


def down_heap(str_deque: Deque):
    index = 0
    while True:
        min_index = get_min_index(str_deque, index)
        if min_index == index:
            break
        else:
            swap(str_deque, index, min_index)
            index = min_index


def get_min_index(str_deque, index):
    dct = {index: str_deque[index]}
    try:
        dct.update({2 * index: str_deque[2 * index]})
    except IndexError:
        pass
    try:
        dct.update({2 * index + 1: str_deque[2 * index + 1]})
    except IndexError:
        pass
    return min(dct, key=dct.get)


def swap(seq, i, j):
    tmp = seq[i]
    seq[i] = seq[j]
    seq[j] = tmp


if __name__ == '__main__':
    main()