from heapq import heappop,heappush
N=int(raw_input())
hp=[]
for i in range(N):
    S=raw_input()
    heappush(hp,S+"{")
ans=""
while len(hp)!=0:
    s=heappop(hp)
    ans+=s[0]
    if len(s)>2:
        heappush(hp,s[1:])
print ans