S = input()
D = [0] * 13

for s in S:
    D[ord(s) - 97] += 1

z = 0
t = 0
p = None

for i in range(13):
    if D[i] == 0:
        z += 1
        p = chr(i + 97)
    elif D[i] == 1:
        continue
    elif D[i] == 2:
        t += 1
    else:
        print('Impossible')
        break
else:
    if z == t == 0:
        for s in 'abcdefghijklm':
            print(s)
    elif z == 1 and t == 1:
        print(p)
    else:
        print('Impossible')