S = input()
cnt = [0]*13
for s in S:
    cnt[ord(s) - 97] += 1

sortedcnt = sorted(cnt)
if sortedcnt == [0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2]:
    for i in range(13):
        if cnt[i] == 0:
            print(chr(i + 97))

elif sortedcnt == [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]:
    for i in range(13):
        print(chr(i + 97))

else:
    print('Impossible')