import heapq

n = int(input())

hp = []
for _ in range(n):
  si = input()
  heapq.heappush(hp, si)

ans = []
while len(hp) > 0:
  cur = heapq.heappop(hp)
  if len(cur) == 1 or len(hp) == 0:
    ans.append(cur)
  else:
    ans.append(cur[0])
    heapq.heappush(hp, cur[1:])

print("".join(ans))