from collections import Counter

S = list(input())

counter = Counter(S)
if max(counter.values()) > 2:
    print("Impossible")
    exit()

S.sort()
s = ''.join(S)
t = "abcdefghijklm"
if s == t:
    for i in range(13):
        print(s[i])
else:
    for i in range(13):
        if t[i] not in s:
            print(t[i])
            break