#include<iostream>
#include<algorithm>
#include <vector>
#include<cmath>
#include<iomanip>
#include<queue>
using namespace std;
typedef long long int lint;
int main() {
	int N, M;
	string S, T;
	cin >> N >> M >> S >> T;
	int sa = 0;
	int sb = 0;
	int ta = 0;
	int tb = 0;
	for (int ia = 0; ia < N; ia++) {
		if (S.at(ia) == 'A') {
			sa++;
		}
		if (S.at(ia) == 'B') {
			sb++;
		}
	}
	for (int ib = 0; ib < M; ib++) {
		if (T.at(ib) == 'A') {
			ta++;
		}
		if (T.at(ib) == 'B') {
			tb++;
		}
	}
	cout << min(sa, ta) + min(sb, tb) << endl;
}