S = list(input())
aToM = [chr(i) for i in range(ord('a'),ord('m')+1)]
aToZ = [chr(i) for i in range(ord('a'),ord('z')+1)]
ans = []
for a in aToM:
	T = ''.join(S) + a
	twoCnt = 0
	oneCnt = 0
	for b in aToM:
		if T.count(b) == 2:
			twoCnt += 1
	for b in aToM:
		if T.count(b) == 1:
			oneCnt += 1
	if twoCnt == 1 and oneCnt + twoCnt * 2 == len(S) + 1:
		ans.append(a)
if len(ans) == 0:
	print('Impossible')
else:
	print('\n'.join(ans))