from collections import Counter as c
s=input()
l=set("abcdefghijklmm")-set(s)
d={j:i for i,j in c(s).items()}

if 2 in d and len(l)==1:
  print(l.pop())
elif not 2 in d and not l:
  print(*sorted(s),sep="\n")
else:
  print("Impossible")