while True:
    try:
        s = input()
        half = len(s) // 2
        s_1 = s[:half]
        s_2 = s[half: len(s)]
        # print(s_1)
        # print(s_2)
        s_1_set = set(s_1)
        s_1_count = []
        for i in s_1_set:
            s_1_count.append(s_1.count(i))
        # print(sorted(s_1_count))
        s_1_answer = len(s_1) - sorted(s_1_count)[-1]

        s_2_set = set(s_2)
        s_2_count = []
        for j in s_2_set:
            s_2_count.append(s_2.count(j))
        # print(sorted(s_2_count))
        s_2_answer = len(s_2) - sorted(s_2_count)[-1]

        answer = s_1_answer + s_2_answer
        print(answer)

    except Exception as e:
        break