import heapq

END = chr(ord('z') + 1)

N = int(input())
S = [input() + END for _ in range(N)]
ans = ''

h = []
for i, s in enumerate(S):
    heapq.heappush(h, (s, i))
while True:
    s, i = heapq.heappop(h)
    if s[0] == END:
        break
    heapq.heappush(h, (s[1:], i))
    ans += s[0]
print(ans)