from string import ascii_lowercase

N = int(input())

strings = []
re = ""

for x in range(N):
    strings.append(input())

"""
ans = ""

def cut(str):
    return str[1:]

while ( not all( x == "" for x in strings) ):
    min = strings[0]

    for x in strings:
        if (min[0] > x[0]):
            min = x

    ans += min[0]
    if (cut(min) == ""):
        strings.pop(strings.index(min))
    else:
        strings[strings.index(min)] = cut(min)

print(ans)
"""

dic = {}

for i in ascii_lowercase:
    dic[i] = 0

for string in strings:
    for x in string:
        dic[x] += 1

for key in dic.keys():
    re += key*dic[key]

print(re)