Description

Input

The first line contains a single integer $t$ ($1 \le t \le 10^4$) — the number of test cases. The description of the test cases follows.

Each test case consists of two lines. The first line contains a single integer $n$ ($1 \le n \le 2 \cdot 10^5$) — the length of the string $s$.

The second line contains the string $s$, consisting of $n$ lowercase English letters.

The sum of $n$ over all test cases does not exceed $2 \cdot 10^5$.

Output

For each test case, output a single integer — the minimum number of operations required to make the string $s$ an anti-palindrome, or $-1$ if this is not possible.

10
10
codeforces
3
abc
10
taarrrataa
10
dcbdbdcccc
4
wwww
12
cabbaccabaac
10
aadaaaaddc
14
aacdaaaacadcdc
6
abccba
12
dcbcaebacccd
 
 
 
 
 
 
 
 
 
 

0
-1
1
1
-1
3
-1
2
2
2

Note

In the first test case, the string "codeforces" is already an anti-palindrome, so the answer is $0$.

In the second test case, it can be shown that the string "abc" cannot be transformed into an anti-palindrome by performing the allowed operations, so the answer is $-1$.

In the third test case, it is enough to swap the second and the fifth characters of the string "taarrrataa", and the new string "trararataa" will be an anti-palindrome, so the answer is $1$.