import sys
s = input()
cnt = [0] * 13
for i in s:
    if ord(i) > ord('m') or ord(i) < ord('a'):
        print("Impossible")
        sys.exit(0)
    else:
        cnt[ord(i) - ord('a')] += 1
cntzero = 0
for i in range(13):
    cntzero += 1 if cnt[i] == 0 else 0
if cntzero >= 2:
    print("Impossible")
elif cntzero == 1:
    for i in range(13):
        if cnt[i] == 0:
            print(chr(i + ord('a')))
else:
    for i in range(13):
        print(chr(i + ord('a')))