S = list(input())
K = 0
M = 0
for i in range(len(S)):
    if chr(97+i) in S:
        K += S.count(chr(97+i))
    if S.count(chr(97+i)) == 0:
        M = chr(97+i)
if M == 0:
    for i in range(13):
        print(chr(97+i))
elif K == 13:
    print(M)
else:
    print("Impossible")