#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>

using namespace std;



int main(){
	int i, j, k;
	int n, m;
	string s, t;
	int na = 0, nb = 0, ma = 0, mb = 0;


	cin >> n >> m;

	cin >> s >> t;

	for (i = 0; i < s.length(); i++) {
		if (s[i] == 'A') {
			na++;
		}
		else {
			nb++;
		}
	}

	for (i = 0; i < t.length(); i++) {
		if (t[i] == 'A') {
			ma++;
		}
		else {
			mb++;
		}
	}

	cout << min(na, ma) + min(nb, mb) << endl;



	getchar();
	getchar();
	return 0;
}