#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
	int N, M; string s, t;
	cin >> N >> M >> s >> t;
	int sa = 0, ta = 0;
	for (int i = 0; i < N; ++i) sa += (s[i] == 'A');
	for (int i = 0; i < M; ++i) ta += (t[i] == 'A');
	int sb = N - sa, tb = M - ta;
	cout << min(sa, ta) + min(sb, tb) << '\n';
	return 0;
}