import heapq

N = int(input())
S = [input() + "{" for _ in range(N)]
heapq.heapify(S)

ans = []
while S:
    X = heapq.heappop(S)
    ans.append(X[0])
    if len(X) > 2:
        heapq.heappush(S, X[1:])

print("".join(ans))