import tables, sets
let S = stdin.readLine
var
  Sct = initCountTable[char]()
  dic, Sst = initSet[char]()
  flg: bool
for s in ('a' .. 'm'):
  dic.incl s
for s in S:
  Sst.incl s
  Sct.inc s
for s in ('a' .. 'm'):
  var
    Sct2 = Sct
    Sst2 = Sst
  Sct2.inc s
  Sst2.incl s
  if Sst2 == dic and Sct2.largest.val >= 2:
    flg = true
    echo s
if not flg: echo "Impossible"