A = 'abcdefghijklm'
S = input()
K = []
for c in A:
	N = []
	T = S + c
	for j in A:
		N.append(T.count(j))
	if N.count(1) == 12 and N.count(2) == 1:
		K.append(c)
print('Impossible' if len(K) == 0 else '\n'.join(K))