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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>

int main(void)
{
  char a[100010];
  int count=0;
  scanf("%s",a);
  int len=strlen(a);
  int j=0;

  int start=0,end=len-1;

  while(start<end){
    // printf("%d %d\n",start,end);
    if(a[start]==a[end]){
      start++;
      end--;
      //  puts("a");
    }else if(a[start]=='x'){
      count++;
      start++;
      //  puts("b");
    }else if(a[end]=='x'){
      count++;
      end--;
      // puts("c");
    }else{
      puts("-1");
      return 0;
    }
  }

  printf("%d\n",count);
  return 0;
}