n = int(input())
r = 0
from heapq import *
q = []
for _ in range(n):
    s = input()+"{"
    q.append(s)
    r += len(s)-1
heapify(q)
ans = []
for i in range(r):
    s = heappop(q)
    ans.append(s[0])
    heappush(q,s[1:])
print("".join(ans))