N = int(input())
import heapq
q = []
for _ in range(N):
    S = input()
    q.append(S)
heapq.heapify(q)
ans = []
while q:
    S = heapq.heappop(q)
    ans.append(S[0])
    if len(S) != 1:
        heapq.heappush(q,S[1:])
print("".join(ans))