n = int(input())
length = 0
words = []
for _ in range(n):
    s = input()
    length += len(s)
    words.append(list(s))

t = ""
for _ in range(length):
    x = min(w for w in words)
    for i,w in enumerate(words):
        if x == w:
            words[i].pop(0)
            if len(words[i]) == 0:
                del words[i]
            break
    t += x
print(t)