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 Python (3.4.3) (judge verdict: Accepted)

# coding: utf-8
# Here your code !
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Mon Oct  9 22:12:40 2017

@author: kitagenbakurou
"""
import numpy as np
import copy

def insert(pos, s, x):
  return x.join([s[:pos], s[pos:] ])

s = input()
N = len(s)

i = 0
j = N - 1
cnt = 0
flag = True
while i < j : 
    if s[i] != s[j] : 
        if s[i] == "x" : 
            cnt += 1
            #s = insert(N - i  , s , "x")
            i += 1
            j += 0
        elif s[j] == "x" : 
            cnt += 1
            #s = insert(i , s , "x")
            i +=0
            j -= 1
        else : 
            flag = False
            break
    else : 
        i += 1
        j -= 1

if flag : 
    print(cnt)
else : 
    print(-1)