def main():
    S = input()

    txt = 'abcdefghijklm'
    strings = sorted(set(S))
    n = len(strings)
    if n < 12:
        print('Impossible')
    elif n == 12:
        for i in range(12):
            if txt[i] != strings[i]:
                print(txt[i])
                break
    else:
        for s in strings:
            print(s)

main()