S = raw_input()
hand = []
for i in range(0, 13):
	hand.append(S[i])
hand.sort()
letter = []
lettercount = []
tmp = ''
for i in range(0, 13):
	if hand[i] == tmp: lettercount[-1] += 1
	else:
		letter.append(hand[i])
		lettercount.append(1)
		tmp = hand[i]
if len(letter) != 7: print 'Impossible'
else:
	notpair = ''
	for i in range(0, 7):
		if lettercount[i] > 2:
			print 'Impossible'
			break
		if lettercount[i] == 1:
			if notpair != '':
				print 'Impossible'
				break
			notpair = letter[i]
		if i == 6: print notpair