package main import ( "bufio" "fmt" "log" "os" "strconv" ) // const abcd = "abcdefghijklmnopqrstuvwxyz" // const ABCD = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" // var dy = [...]int{1, 1, 0, -1, -1, -1, 0, 1} // var dx = [...]int{0, 1, 1, 1, 0, -1, -1, -1} // var dx = [...]int{0, 1, 0, -1} // var dy = [...]int{1, 0, -1, 0} var inf int = 1e13 var mod = 1000000007 var next = newScanner() // --------------------------------------------------------- func main() { log.SetFlags(log.Lshortfile) S := next.String() count := map[byte]int{} var ans string if len(S)%2 == 0 { ans = "Impossible" } else { for i := range S { count[S[i]]++ } for k, v := range count { if v == 1 && ans == "" { ans = string(k) } else if v != 2 || (ans != "" && v == 1) { ans = "Impossible" break } } } fmt.Println(ans) } // --------------------------------------------------------- // Pair is... type Pair struct { a, b int } // Pairs is sorted by []Pair struct type Pairs []Pair func (p Pairs) Len() int { return len(p) } func (p Pairs) Swap(i, j int) { p[i], p[j] = p[j], p[i] } func (p Pairs) Less(i, j int) bool { if p[i].a < p[j].a { return true } else if p[i].a == p[j].a { return p[i].b < p[j].b } return false } // ------int method------------------------- func in(c, a, z int) bool { return c >= a && c < z } func btoi(b bool) int { if b { return 1 } return 0 } func itob(a int) bool { if a == 0 { return false } return true } func max(a ...int) int { r := a[0] for i := 0; i < len(a); i++ { if r < a[i] { r = a[i] } } return r } func min(a ...int) int { r := a[0] for i := 0; i < len(a); i++ { if r > a[i] { r = a[i] } } return r } func sum(a []int) int { r := 0 for i := 0; i < len(a); i++ { r += a[i] } return r } func pro(a []int) int { r := 1 for i := 0; i < len(a); i++ { r *= a[i] } return r } func fill(a []int, n int) []int { for i := 0; i < len(a); i++ { a[i] = n } return a } func minmax(a, b int) (int, int) { if a > b { return b, a } return a, b } func abs(a int) int { if a < 0 { return -a } return a } // ---------- buffered scanner ----------------------------------------- func iferr(err error) { if err != nil { panic(err) } } type scanner struct { r *bufio.Reader buf []byte p int } func newScanner() *scanner { rdr := bufio.NewReaderSize(os.Stdin, 10000) return &scanner{r: rdr} } func (s *scanner) next() string { s.pre() start := s.p for ; s.p < len(s.buf); s.p++ { if s.buf[s.p] == ' ' { break } } result := string(s.buf[start:s.p]) s.p++ return result } func (s *scanner) Line() string { s.pre() start := s.p s.p = len(s.buf) return string(s.buf[start:]) } func (s *scanner) String() string { return s.next() } func (s *scanner) Int() int { v, e := strconv.Atoi(s.next()) iferr(e) return v } func (s *scanner) Ints(n int) []int { r := make([]int, n) for i := 0; i < n; i++ { r[i] = s.Int() } return r } func (s *scanner) Int64() int64 { v, e := strconv.ParseInt(s.next(), 10, 64) iferr(e) return v } func (s *scanner) Uint64() uint64 { v, e := strconv.ParseUint(s.next(), 10, 64) iferr(e) return v } func (s *scanner) Float64() float64 { v, e := strconv.ParseFloat(s.next(), 64) iferr(e) return v } func (s *scanner) pre() { if s.p >= len(s.buf) { s.readLine() s.p = 0 } } func (s *scanner) readLine() { s.buf = make([]byte, 0) for { l, p, e := s.r.ReadLine() iferr(e) s.buf = append(s.buf, l...) if !p { break } } }