package main

import (
	"fmt"
)

func main() {
	var str string
	fmt.Scan(&str)
	m1 := make(map[byte]int, len(str)/2)
	m2 := make(map[byte]int, len(str)/2)
    for i:=0;i<len(str)/2;i++{
        m1[str[i]]++
        m2[str[len(str)/2+i]]++
    }
    var max1, max2, sum1, sum2 int
    for _,v := range m1{
        if v > max1{
            max1 = v
        }
        sum1 += v
    }
    for _,v := range m2{
        if v > max2{
            max2 = v
        }
        sum2 += v
    }
	fmt.Print(sum1-max1+sum2-max2)
}