Given a string, what is the minimum number of adjacent swaps required to convert a string into a palindrome. If not possible, return -1.

Example 1:

Input: "mamad"

Output: 3

Example 2:

Input: "asflkj"

Output: -1

Example 3:

Input: "aabb"

Output: 2

Example 4:

Input: "ntiin"

Output: 1

Explanation: swap 't' with 'i' => "nitin"