#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

int gcd(int x, int y) { return y ? gcd(y, x % y) : x; }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
int lcm(int x, int y) { return x / gcd(x, y) * y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int n, m;
	string s, t;
	cin >> n >> m >> s >> t;

	sort(begin(s), end(s));
	sort(begin(t), end(t));

	int nn = min((int)s.size(), (int)t.size());

	pair<int, int> cntS = { 0, 0 };
	for (int i = 0; i < (int)s.size(); i++) {
		if (s[i] == 'A') {
			cntS.first++;
		} else {
			cntS.second++;
		}
	}

	pair<int, int> cntT = { 0, 0 };
	for (int i = 0; i < (int)t.size(); i++) {
		if (t[i] == 'A') {
			cntT.first++;
		} else {
			cntT.second++;
		}
	}

	int okA = max(cntS.first, cntT.first) - abs(cntS.first - cntT.first);
	int okB = max(cntS.second, cntT.second) - abs(cntS.second - cntT.second);

	cout << min(nn, okA + okB) << endl;
	return 0;
}