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