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