S = input()
cnt = [S.count(chr(ord("a") + i)) for i in range(13)]
if max(cnt) == 2 and cnt.count(0) == 1:
    print(chr(ord("a") + cnt.index(0)))
elif cnt.count(1) == 13:
    for i in range(13):
        print(chr(ord("a") + i))
else:
    print("Impossible")