s = input()
count = {}
for c in s:
    if c not in count:
        count[c] = 0
    count[c] += 1
if len(count) != 7:
    print('Impossible')
    exit()
values = list(count.values())
values.sort()
if values[0] != 1 or values[1] != 2 or values[6] != 2:
    print('Impossible')
    exit()
for key in count:
    if count[key] == 1:
        print(key)