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) ):
    min = strings[0]

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

    ans.append(min[0])
    strings[strings.index(min)] = cut(min)

print(ans)