import tables

proc impossible =
  echo "Impossible"
  quit()

let S = stdin.readLine
var dic = initCountTable[char]()

for s in S:
  dic.inc s

if dic.largest.val >= 3:
  impossible()

for k, v in dic:
  if k notin ('a' .. 'm'):
    impossible()

for s in ('a' .. 'm'):
  var dic2 = dic
  dic2.inc s
  if dic2.len >= 13:
    echo s