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 Java8 (OpenJDK 1.8.0) (judge verdict: Runtime Error)

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		int ans = 0, l = 0, r = n - 1;
		if(n == 1) {
			System.out.println(0);
			return;
		}
		for(; ; ) {
			if(s.charAt(l) == s.charAt(r)) {
				l++; r--;
			} else {
				if(s.charAt(l) != 'x' && s.charAt(r) != 'x') {
					System.out.println(-1);
					return;
				} else {
					if(s.charAt(l) == 'x') {
						l++;
						ans++;
						if(l == r) {
							System.out.println(ans);
							return;
						}
					}
					if(s.charAt(r) == 'x') {
						r--;
						ans++;
						if(l == r) {
							System.out.println(ans);
							return;
						}
					}
				}
			}
		}
	}
}