S=''.join(sorted(input()))
A='abcdefghijklm'
o='Impossible'
Z=set()
for i in range(13):
    for j in range(13):
        if A in S[:i]+A[j]+S[i:]:
            o=''
            Z.add(A[j])
else:
    if o:print(o)
print('\n'.join(sorted(Z)))