from collections import defaultdict
kokushi = "abcdefghijklm"
s = input()
dd = defaultdict(int)
for ss in s:
    dd[ss] += 1
    if dd[ss] == 3:
        print("Impossible")
        exit()
if len(dd) == 13:
    for s in kokushi:
        print(s)
    exit()
elif len(dd) == 12:
    for ss in kokushi:
        if dd[ss] == 0:
            print(key)
            exit()
else:
    print("Impossible")