package main

import . "fmt"
import . "strings"

func main() {
	var n,m,s,t string
	Scan(&n,&m,&s,&t)
	Println(min(Count(s,"A"),Count(t,"A"))+min(Count(s,"B"),Count(t,"B")))
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}