import collections
S = list(input())
cnt = collections.Counter(S)
a = 'abcdefghijklm'
if len(S) != 13:
    print('Impossible')
    exit()

if len(cnt) == 13:
    print(*list(a),sep='\n')
elif len(cnt) == 12:
    for c in a:
        if not c in cnt:
            print(c)
            break
else:
    print('Impossible')