import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		new Main().run();
	}

	void run() {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		String str1 = sc.next();
		String str2 = sc.next();
		int[] cnt1 = new int[2];
		int[] cnt2 = new int[2];
		for (char c : str1.toCharArray()) {
			if (c == 'A')
				++cnt1[0];
			else
				++cnt1[1];
		}
		for (char c : str2.toCharArray()) {
			if (c == 'A') {
				++cnt2[0];
			} else {
				++cnt2[1];
			}
		}
		int a = Math.min(cnt1[0], cnt2[0]);
		int b = Math.min(cnt1[1], cnt2[1]);
		tr(cnt1, cnt2);
		System.out.println(a + b);
	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
}