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

for i in xrange(N):
    s = S.pop(0)
    j = 0
    for si in s:
        for i in xrange(j, len(T)):
            if T[i] > si:
                T = T[:i] + si + T[i:]
                j = i + 1
                break
        else:
            T += si
            j = i + 1
print T