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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

var s:ansistring;
    i:longint;
    n,l,r:longint;
    ans:int64;
begin
  readln(s);
  n:=length(s);
  l:=1;
  r:=n;
  while l<r do
  begin
    if (s[l]<>s[r]) then
    begin
      if (s[l]='x') then
      begin
        inc(ans);
        inc(l);
      end else
      if (s[r]='x') then
      begin
        inc(ans);
        dec(r);
      end else
      begin
        writeln(-1);
        exit;
      end;
    end else
    begin
      inc(l);
      dec(r);
    end;
  end;
  writeln(ans);
end.