import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int sa = 0;
        int sb = 0;
        for (char c : sc.next().toCharArray()) {
            if (c == 'A') {
                sa++;
            } else {
                sb++;
            }
        }
        int ta = 0;
        int tb = 0;
        for (char c : sc.next().toCharArray()) {
            if (c == 'A') {
                ta++;
            } else {
                tb++;
            }
        }
        System.out.println(Math.min(sa, ta) + Math.min(sb, tb));
    }
}