while True:
    n=int(raw_input().strip())
    if n==0:
        break
    list1=map(str,raw_input().strip().split())
    list2=[]
    list3=[]
    list4=[]
    list5=[]
    list6=[]
    for value in list1:
         list2.append(list(value))
    for value in list2:
        list3.append(sorted(value))
    for value in list3:
        list4.append(''.join(value))
    for i in range(len(list4)): 
        if list4.count(list4[i])==1: 
            list5.append(i)
    for i in list5:
        list6.append(list1[i]) 
    if list6:
        list6.sort()
        print ' '.join(list6)
    else:
        print 'None'