#include<iostream>
#include <algorithm>
#include<string>
#include <bitset>
#include <vector>
#include <functional>
#include <climits>
#include <iomanip>
#include <utility>
using namespace std;
typedef pair <int, int> pii;
int main()
{

	//int a = 0, b = 0, c = 0, d = 0, e = 0, f = 0, g = 0, h = 0, ans = 0;
	int a = 0, b = 0, c = 0, d = 0, e = 0, f = 0, g = 0, h = 0, i = 0, j = 0, k = 0, l = 0, ans = 0;
	//cout << LONG_MAX << endl;
	string s, t;
	//long long n, A[1000000000];
	long long n, m;
	//int   y[100001], z[100001], x[10001] = {};
	//pii y[100001];
	//pair<int, float> pii[100001];
	int x[1003];
	cin >> n;
	cin >> m;
	//string s;
	cin >> s;
	for (a = 0; a < s.length(); a++)
	{
		if (s[a] == 'A')
		{
			b++;
		}
		else
		{
			c++;
		}
	}
	cin >> s;
	for (a = 0; a < s.length(); a++)
	{
		if (s[a] == 'A')
		{
			d++;
		}
		else
		{
			e++;
		}
	}
	f += min(b, d);
	f += min(c, e);
	////std::cout << std::fixed;
	//cout << std::setprecision(20) << << endl;
	cout << f << endl;

	return 0;
}