#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <fstream>
#include <set>
#include <utility>
#include <algorithm>
#include <queue>
#include <stack>
#include <deque>
#include <numeric>
#include <sstream>
#include <list>
#include <map>

#define rep(i,p,n) for(int i=(int)p;i<(int)n;i++)
#define repp(i,p,n) for(int i=(int)p;i>=(int)n;i--)
#define Sort(x) sort(x.begin(),x.end());
#define ll long long 
#define INF 2000000000

using namespace std;
int main() {
	int n, m;
	int ua=0, ub=0, da=0, db=0;
	cin >> n >> m;
	rep(i, 0, n) {
		char c;
		cin >> c;
		if (c == 'A')ua++;
		else if (c == 'B')ub++;
	}

	rep(i, 0, m) {
		char c;
		cin >> c;
		if (c == 'A')da++;
		else if (c == 'B')db++;
	}

	cout << min(ua, da) + min(ub, db) << endl;
	
	
	
	return 0;
}