from collections import Counter
S = input()
c = Counter(S)
values = sorted(list(c.values()))
if values[0] != 1:
    print('Impossible')
    exit()
if values[1] != 2:
    print('Impossible')
    exit()
if values[-1] != 2:
    print('Impossible')
    exit()
for key, value in zip(c.keys(), c.values()):
    if value == 1:
        print(key)