#include <iostream>
#include <string>
#include <map>
using namespace std;
int main(){
	int N, M;
	cin >> N >> M;
	string S;
	cin >> S;
	string T;
	cin >> T;
	map<char, int> mp1;
	for (int i = 0; i < N; i++){
		mp1[S[i]]++;
	}
	map<char, int> mp2;
	for (int i = 0; i < M; i++){
		mp2[T[i]]++;
	}
	cout << min(mp1['A'], mp2['A']) + min(mp1['B'], mp2['B']) << endl;
}