Problem:
Score : 400 points

Problem Statement

We have a string s consisting of lowercase English letters.
Snuke can perform the following operation repeatedly:

Insert a letter x to any position in s of his choice, including the beginning and end of s.

Snuke's objective is to turn s into a palindrome.
Determine whether the objective is achievable. If it is achievable, find the minimum number of operations required.

Notes

A palindrome is a string that reads the same forward and backward.
For example, a, aa, abba and abcba are palindromes, while ab, abab and abcda are not.

Constraints

1 \leq |s| \leq 10^5

s consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

s

Output

If the objective is achievable, print the number of operations required.
If it is not, print -1 instead.

Sample Input 1

xabxa

Sample Output 1

2

One solution is as follows (newly inserted x are shown in bold):

xabxa → xaxbxa → xaxbxax

Sample Input 2

ab

Sample Output 2

-1

No sequence of operations can turn s into a palindrome.

Sample Input 3

a

Sample Output 3

0

s is a palindrome already at the beginning.

Sample Input 4

oxxx

Sample Output 4

3

One solution is as follows:

oxxx → xoxxx → xxoxxx → xxxoxxx

Solution in Go (1.6) (judge verdict: Runtime Error)

package main

import (
	"math/rand"
	"time"
	"os"
	"bufio"
	"fmt"
	"strconv"
)

var(
	inf = 10000000071000000
	stdin = bufio.NewReader(os.Stdin)
	mod = 1000000007
	mod9 = 1000000009
	//////////////////////////////////
	stack []byte
)

func init()  {
	rand.Seed(time.Now().UnixNano())
}

type zahyo struct {
	x int
	y int
}

func main() {
	s := gostring()
	count := 0
	l,r := 0,len(s)-1
	for {
		if l == r{break}
		if s[l] == s[r]{
			l++;r--
		} else {
			if s[l] == 'x' {
				count ++
				l++
			} else if s[r] == 'x'{
				count ++
				r --
			} else {
				fmt.Println(-1)
				os.Exit(0)
			}
		}
	}
	fmt.Println(count)
}


//||||||||||||||||||||||||||入力|||||||||||||||||||||||||||||||||||||||

//次のスペースか改行まで読み込む
func gostring() string {
	byte_ls := make([]byte,0)
	for  {
		b, _ := stdin.ReadByte()
		if b == 32 || b == 10 || b == 0{
			return string(byte_ls)
		} else if b == 13 {
			continue
		} else {
			byte_ls = append(byte_ls,b)
		}
	}
}

//上の関数のintバージョン
func goint() int {
	n,_ := strconv.Atoi(gostring())
	return n
}

//数字一行
func intLine(n ,a int) []int {
	ls := make([]int,n)
	for i,_ := range ls{
		ls[i] = goint() + a
	}
	return ls
}

//|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

func sum(a ...int) int {
	ans := 0
	for i:=0;i<len(a);i++{
		ans += a[i]
	}
	return ans
}

func min(a ...int) int {
	ans := a[0]
	for i:=1;i<len(a);i++{
		if ans > a[i]{
			ans = a[i]
		}
	}
	return ans
}

func abs(n int) int {
	if n >= 0{
		return n
	} else {
		return -n
	}
}

func max(a ...int) int {
	ans := a[0]
	for i:=1;i<len(a);i++{
		if ans < a[i]{
			ans = a[i]
		}
	}
	return ans
}

func intList(n,k int) []int {
	ls := make([]int,n)
	for i:=0;i<n;i++{
		ls[i] = k
	}
	return ls
}