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: Wrong Answer)


def check_pa(word)
    #word = word.to_s
      size = word.length / 2
        return ( word[0..size] == word.reverse[0..size] )
end

a = gets.chomp.split("")#.map(&:to_i)
if check_pa(a)
  p 0
elsif !a.include?("x")
  p -1
end

tmp = 0

for i in 0..(a.size-1)
  tmp+= 1 if a[i] == "x" && a[a.size-1-i] == "x" 
end

if check_pa(a.select{|t| t != "x"})
  p (a.select{|t| t== "x"}.size - tmp)
else
  p -1
end