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 Ruby (2.3.3) (judge verdict: Runtime Error)

str = gets().split("")
n = str.length-1

countx = 0

flag = 0

for i in 0..n-1
	if str[i] == "x"
		countx = countx + 1
	end
end

str_alt = Array.new(n-countx)
k=0

for j in 0..n-1
	if str[j] != "x"
		str_alt[k] = str[j]
		k = k + 1
	end 
end

countc = 0
m = 0

n_alt = str_alt.length

if n_alt  %2 == 0
	m = str_alt.length / 2
	for l in 0..m-1
		if str_alt[l] == str_alt[m-1]
			countc = countc + 1
		end
		if str_alt[l] != str_alt[str_alt.length-1-l]
			flag = 1
		end
	end
elsif n_alt %2 == 1
	m = str_alt.length / 2 + 1
	for l in 0..m-1
		if str_alt[l] == str_alt[m-1]
			countc = countc + 1
		end
		if str_alt[l] != str_alt[str_alt.length-1-l]
			flag = 1
		end
	end
end

o = 0
while countc > 0
	if str[o] == str_alt[m-1]
		countc = countc -1
	end
	o = o + 1
end 

countx_ue = 0
countx_sita = 0

for q in 0..n-1
	if str[q] == "x" && q<o
		countx_sita = countx_sita + 1
	end
	if str[q] == "x" && q>=o
		countx_ue = countx_ue + 1
	end
end


if flag == 0
	pre_ans = countx_sita - countx_ue
	ans = pre_ans.abs
	if 
	puts(ans)
elsif flag == 1
	puts("-1")
end