import heapq

N = input()
S = []
for i in xrange(N):
    heapq.heappush(S, raw_input())

ans = ''
while len(S) > 0:
    s = heapq.heappop(S)
    ans += s[0]
    if len(s) > 1:
        heapq.heappush(S, s[1:])
print ans