package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strconv"
)

var iost *Iost

type Iost struct {
	Scanner *bufio.Scanner
	Writer  *bufio.Writer
}

func NewIost(fp io.Reader, wfp io.Writer) *Iost {
	const BufSize = 2000005
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, BufSize), BufSize)
	return &Iost{Scanner: scanner, Writer: bufio.NewWriter(wfp)}
}
func (i *Iost) Text() string {
	if !i.Scanner.Scan() {
		panic("scan failed")
	}
	return i.Scanner.Text()
}
func (i *Iost) Atoi(s string) int                 { x, _ := strconv.Atoi(s); return x }
func (i *Iost) GetNextInt() int                   { return i.Atoi(i.Text()) }
func (i *Iost) Atoi64(s string) int64             { x, _ := strconv.ParseInt(s, 10, 64); return x }
func (i *Iost) GetNextInt64() int64               { return i.Atoi64(i.Text()) }
func (i *Iost) Atof64(s string) float64           { x, _ := strconv.ParseFloat(s, 64); return x }
func (i *Iost) GetNextFloat64() float64           { return i.Atof64(i.Text()) }
func (i *Iost) Print(x ...interface{})            { fmt.Fprint(i.Writer, x...) }
func (i *Iost) Printf(s string, x ...interface{}) { fmt.Fprintf(i.Writer, s, x...) }
func (i *Iost) Println(x ...interface{})          { fmt.Fprintln(i.Writer, x...) }
func isLocal() bool                               { return os.Getenv("I") == "IronMan" }
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	if isLocal() {
		fp, _ = os.Open(os.Getenv("END_GAME"))
	}
	iost = NewIost(fp, wfp)
	defer func() {
		if isLocal() {
			iost.Println(recover())
		}
		iost.Writer.Flush()
	}()
	solve()
	for i := 0; isLocal() && i < 100; i++ {
		iost.Println("-----------------------------------")
		solve()
	}
}
func solve() {
	s := iost.Text()
	n := len(s)
	if !isPalindrome(s) {
		iost.Println(n)
		return
	}
	cnt := make([]int, 26)
	for i := 0; i < n; i++ {
		cnt[s[i]-'a']++
	}
	odd := make([]int, 0)
	even := make([]int, 0)
	for i := 0; i < 26; i++ {
		if cnt[i] == 0 {
			continue
		}
		if cnt[i]%2 == 0 {
			even = append(even, cnt[i])
			continue
		}
		odd = append(odd, cnt[i])
	}
	switch {
	case len(even)+len(odd) == 1:
		if n%2 == 0 {
			iost.Println(0)
			return
		}
		iost.Println(-1)
	case n == 3:
		iost.Println(-1)
	default:
		iost.Println(n - 2)
	}
}
func isPalindrome(s string) bool {
	l := 0
	r := len(s) - 1
	for l < r {
		if s[l] != s[r] {
			return false
		}
		l++
		r--
	}
	return true
}