s = list(input())

count_list = []
for e in s:
    count_list.append(s.count(e))

if count_list.count(1) == 13:
    for e in sorted(s):
        print(e)
elif (count_list.count(1) == 11) and (count_list.count(2) == 2):
    for w in list('abcdefghijklm'):
        if w in s:
            continue
        else:
            print(w)
            break
else:
    print('Impossible')