S=raw_input()
s='abcdefghijklm'
L=[]
for a in s:
    L.append(S.count(a))
if L.count(2)>1 or L.count(0)>1:
    print 'Impossible'
elif L.count(0)==1:
    num=L.index(0)
    print s[num]
else:
    for a in s:
        print a