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)


ary = gets.chomp
len = ary.size
fid = 0
lid = len-1
count = 0
flg = 0
while fid <= lid
  cntf = 0
  while fid < len and ary[fid] == "x"
    fid += 1
    cntf += 1
  end
  cntl = 0
  while lid > -1 and ary[lid] == "x"
    lid -= 1
    cntl += 1
  end
  if (fid > lid) or (ary[fid] != ary[lid])
    flg = -1
    break
  end
  count += (cntl- cntf).abs
  fid += 1
  lid -= 1
end
if flg > -1
  puts count
else
  puts -1
end