#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <cstring>
#include <queue>
#include <stack>
#include <functional>
#include <math.h>
#include <iomanip>
using namespace std;
#define Would
#define you
const int INF = 999999999;
const int MOD = 1e9 + 7;
const double pi = 3.141592653589793238;

int main() {
	int a, b, ans = 0, ans2 = 0;
	string s, h;
	cin >> a >> b >> s >> h;
	for (int i = 0; i < a; ++i) {
		if (s[i] == 'A') { ++ans; }
	}
	for (int i = 0; i < b; ++i) {
		if (h[i] == 'A') { ++ans2; }
	}
	cout << min(ans, ans2) + min(s.length() - ans, h.length() - ans2) << endl;
}