from collections import defaultdict
s = input()
dd = defaultdict(int)
for ss in s:
    dd[ss] += 1
    if dd[ss] >= 3:
        print("Impossible")
        exit()
if len(dd) != 7:
    print("Impossible")
    exit()
for key, value in dd.items():
    if value == 1:
        print(key)