#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>
#include <ctype.h>
using namespace std;

//#include<bits/stdc++.h>

int main() {
	
	int n, m;
	cin >> n >> m;
	string p, q;
	cin >> p >> q;
	int a = 0, b = 0;
	for (int i = 0; i < p.size(); i++) {

		if (p[i] == 'A')a++;
		else b++;

	}
	int c = 0, d = 0;
	for (int i = 0; i < q.size(); i++) {

		if (q[i] == 'A')c++;
		else d++;

	}
	cout << min(a, c) + min(b, d) << endl;


	return 0;
}