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 Ruby (2.3.3) (judge verdict: Accepted)

s=gets.chomp
ss=s.delete ?x
c=true
(ss.size/2).times do |i|
  if ss[i]!=ss[ss.length-1-i]
    c=false
  end
end
cc=0
if c
  cc=0
  t=s.size-1
  tt=0
  while true do
    break if tt>=t
    if s[t]==?x
      if s[tt]==?x
        t-=1
        tt+=1
      else
        t-=1
        cc+=1
      end
    else
      if s[tt]==?x
        tt+=1
        cc+=1
      else
        t-=1
        tt+=1
      end
    end
  end
end
puts c ? cc : -1