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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<iostream>
#include<vector>
#include<algorithm>
#include<map>
#include<queue>
using namespace std;

int main(){
	string s ;
	cin >> s;
	string tmp = "";
	for(int i=0;i<s.size();++i){
		if(s[i] != 'x'){
			tmp += s[i];
		}
	}
	
	string tmptmp = tmp; 
	reverse(tmp.begin(),tmp.end());
	if(tmptmp == tmp){
		int res = 0;
		for(int i=0,j=s.size()-1;i <= j ;){
			if(s[i] != s[j]){
				res++;
				if(s[i] == 'x') i++;
				else if(s[j] == 'x') j--;
			}else{
				i++;
				j--;
			}
		}
		cout << res <<endl;
	}else{
		cout << -1 <<endl;
	}
	
	return 0;

}