import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int M = scan.nextInt();
		String S = scan.next();
		String T = scan.next();
		scan.close();
		int a1 = 0;
		int b1 = 0;
		int a2 = 0;
		int b2 = 0;
		for(int i = 0; i < N; i++) {
			char c = S.charAt(i);
			if(c == 'A') {
				a1 ++;
			}else {
				b1 ++;
			}
		}
		for(int i = 0; i < M; i++) {
			char c = T.charAt(i);
			if(c == 'A') {
				a2 ++;
			}else {
				b2 ++;
			}
		}
		int ans = Math.min(a1, a2) + Math.min(b1, b2);
		System.out.println(ans);
	}
}