#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
#define dunk(a) cout << (a) << endl
using namespace std;
typedef long long ll;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n, m;
	cin >> n >> m;
	string S, T;
	cin >> S >> T;//A->muji  B->gara

	int Sa, Sb, Ta, Tb;

	Sa = count(all(S), 'A');
	Sb = count(all(S), 'B');
	Ta = count(all(T), 'A');
	Tb = count(all(T), 'B');

	int ans = min(Sa, Ta) + min(Sb, Tb);

	dunk(ans);

	return 0;
}