s_set = set(input())
kokushi_set = set("abcdefghijklm")

if len(s_set) == len(kokushi_set):
    for k in sorted(kokushi_set):
        print(k)
elif len(kokushi_set - s_set) == 1:
    print(list(kokushi_set - s_set)[0])
else:
    print("Impossible")