from collections import Counter
alp = "abcdefghijklm"
S = input()
chkflg = 0
for x in Counter(list(S)).values():
    if x > 2 or chkflg > 1:
        print("Impossible")
        exit()
    elif x == 2:
        chkflg += 1
if set(list(alp)) == set(list(S)):
    for x in list(alp):
        print(x)
else:
    res = set(list(alp)) - set(list(S))
    for x in sorted(res):
        print(x)