#python 3

def anagram(s):
      if len(s)%2 != 0:
        return -1
      mid = int(len(s)/2)
      s1 = list(s[:mid])
      s2 = list(s[mid:])
      counter = 0
      for i in s1:
        if i in s2:
          s2.remove(i)
        else:
          counter += 1
      return counter