def anagram(s):
    if len(s) % 2 == 1:
        return -1
    s1 = list(s[:len(s) // 2])
    s2 = list(s[len(s) // 2:])
    letters = set(s1 + s2)
    same = 0
    for letter in letters:
        same += min(s1.count(letter), s2.count(letter))
    return (len(s1) + len(s2) - 2 * same) // 2