s = list(input())
l = [0] * 30
for i in range(13):
    l[ord(s[i]) -97] += 1

if sum(l[13:]) > 0:
    print('Impossible')
    exit()

w = 0
ans = [0] * 13
for i in range(13):
    n = ord(s[i])-97
    ans[n] += 1
    if ans[n] == 2:
        w += 1

if w >1:
    print('Impossible')
    exit()
elif w == 0:
    for i in range(13):
        print(chr(i+97))
    exit()
else:
    for i in range(13):
        if ans[i] == 0:
            a = i+97

print(chr(a))