wN = input()
S = [raw_input()[::-1] for _ in xrange(N)]

ans = ''
while len(S) > 0:
    min_s = 'zzz'
    min_i = []
    for i, s in enumerate(S):
        if s[-1] < min_s:
            min_s = s[-1]
            min_i = [i]
        elif s[-1] == min_s:
            min_i.append(i)
            
    min_i = min(min_i, key=lambda i:S[i][::-1]) if len(min_i) > 1 else min_i[0]
    ans += S[min_i][-1]
    if len(S[min_i]) == 1:
        S.pop(min_i)
    else:
        S[min_i] = S[min_i][:-1]

print ans