N=int(input())
S=[input() for i in range(N)]

SUM=sum([len(s) for s in S])

for i in range(N):
    S[i]+="{"

ANS=""

while S:
    S.sort()
    if S[0]=="":
        S=S[1:]
    else:
        ANS+=S[0][0]
        S[0]=S[0][1:]

print(ANS[:SUM])