#yuki_548

r='abcdefghijklm'
s=raw_input()
l=[]
for x in r:
 l.append(s.count(x))

if l.count(2)>=2 or l.count(0)>=2:
 print 'Impossible'
elif l.count(2)==1 and l.count(0)==1:
 pos=l.index(0)
 print r[pos]
elif l.count(2)==0 and l.count(0)==0:
 for i in xrange(13):
  print r[i]