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)
}

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