s = input()
base = "abcdefghijklm"
li = []

for i in base:
    li.append(s.count(i))

if li.count(1) == 13:
    for i in base:
        print(i)
elif li.count(2) == 1 and li.count(0) == 1 and li.count(1) == 11:
    print(base[li.index(0)])
else:
    print('Impossible')