import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
S=[input() for _ in range(n)]
import heapq
H=[]
ans=""
for i in range(n):
  heapq.heappush(H,S[i]+"~")
while H:
  a=heapq.heappop(H)
  ans+=a[0]
  if len(a)>2:
    heapq.heappush(H,a[1:])
print(ans)