N = int(raw_input())
S = sorted([raw_input() for i in xrange(N)])
M = sum(len(s) for s in S)
T = ""

for loop in xrange(M):
    T += S[0][0]
    S[0] = S[0][1:]
    if len(S[0]) == 0: S.pop(0)
    S = sorted(S)
print T