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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php
error_reporting(0);
$N = trim(fgets(STDIN));
//$A = explode(" ",trim(fgets(STDIN)));
//list($N,$M) = explode(" ",trim(fgets(STDIN)));
if (chk($N)) {
  //最初から回文
  printf("%d\n",0);
  exit;
}
if (strpos($N,"x")===false) {
  //回文でないやつにxがない場合は変えられない
  printf("%d\n",-1);
  exit;
}
$cnt = substr_count($N,"x");
$new = str_replace("x","",$N);
if (chk($new)) {
  for($i=1;$i<=$cnt;$i++) {
    //printf("%s\n",str_replace("x","",$N,$i));
    if (chk(str_replace("x","",$N,$i))) {
      printf("%d\n",$i);
      exit;
    }
  }
}
//xなしで回文にならない場合は不可
printf("%d\n",-1);

function chk($N) {
$rev = strrev($N);
if ($rev == $N)
  return true;
return false;
}