from collections import Counter

S = list(input())

S.sort()
s = ''.join(S)
t = "abcdefghijklm"
ans = set()
if s == t:
    for i in range(13):
        print(s[i])
else:
    for i in range(13):
        if t[i] not in s:
            ans.add(t[i])
    if len(ans) == 1:
        print(list(ans)[0])
    else:
        print("Impossible")