# No.548 国士無双
s = input()
cards = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm']
nums = [0] * 13

for i in range(13):
    nums[i] = s.count(cards[i])

if max(nums) == 1:
    for i in cards:
        print(i)
elif max(nums) == 2 and nums.count(2) == 1:
    print(cards[nums.index(0)])
else:
    print('Impossible')