n = int(input())
words = []
for i in range(n):
    words.append(input().strip())
words = [w+'zzzz' for w in words]

ans = ''
while len(words) > 0:
    words.sort()
    ans += words[0][0]
    if len(words[0]) == 5:
        words.pop(0)
    else:
        words[0] = words[0][1:]

print(ans)