N = int(input())
cnt = 0
S = []
for i in range(N):
    temp = [ord(s) - ord("a") for s in input()]
    temp.append(27)
    S.append(temp)
    cnt += len(temp) - 1

S.sort()
ans = []
for _ in range(cnt):
    v = S[0].pop(0)
    ans.append(chr(v + ord("a")))
    S.sort()

print(*ans, sep="")