N = int(input())
strings = []
for x in range(N):
    strings.append(input())

ans = ""

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

while ( all( x == "" for x in strings) ):
    index = 0
    min = strings[0]

    for x in range(len(strings)):
        if (min > x[index]):
            min = x
        index += 1
# yabai

    ans.append(min[:1])
    strings[index] = cut(min)

print(ans)