def checkPalindrome(s):
    for i in range(len(s) // 2):
        if s[i] != s[len(s) - i - 1]:
            return False
    return True

def palindromeIndex(s):
    idx = -1
    # s is palindrome
    if checkPalindrome(s):
        return -1
        
    # find the first character index that does not match
    for i in range(len(s) // 2):
        if s[i] == s[len(s) - i - 1]:
            continue
        else:
            idx = i
            break
    
    # drop the first character
    sub_s_1 = s[(idx+1) : (len(s) - idx)]
    if checkPalindrome(sub_s_1):
        return idx
    
    # drop the last character
    sub_s_2 = s[idx : (len(s) - idx - 1)]
    if checkPalindrome(sub_s_2):
        return len(s) - idx - 1

    return -1