import java.util.*;

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