# coding: utf-8
# Your code here!

n = int(input())
lst = []
t = ""
s_length = 0

for i in range(n):
    s = input()
    s_length += len(s)
    lst.append(s+"z")

for i in range(s_length):
    lst.sort()
    t += lst[0][0]
    if len(lst[0])==2:
        del lst[0]
    else:
        lst[0] = lst[0][1:]

print(t)