package net.ipipip0129.kotlin.yukicoder

import kotlin.math.min

fun abCount(charArray: CharArray): Array<Int> {
    var aCount = 0
    var bCount = 0
    charArray.forEach {
        when (it) {
            'A' -> aCount++
            'B' -> bCount++
        }
    }
    return arrayOf(aCount, bCount)
}

fun main(args: Array<String>) {
    val numArray = readLine()!!.split(" ")
    val numN = numArray[0].toInt()
    val numM = numArray[1].toInt()

    val sCountArray = abCount(readLine()!!.toCharArray())
    val tCountArray = abCount(readLine()!!.toCharArray())

    println(min(sCountArray[0], tCountArray[0]) + min(sCountArray[1], tCountArray[1]))
}