#include <bits/stdc++.h>
#include <assert.h>

using namespace std;

int main()
{
	int n, m;
	string s, t;
	cin >> n >> m >> s >> t;
	int sa = 0, sb = 0, ta = 0, tb = 0;
	for (int i = 0; i < n; i++)
		if (s[i] == 'A')
			sa++;
		else
			sb++;
	for (int i = 0; i < m; i++)
		if (t[i] == 'A')
			ta++;
		else
			tb++;
	cout << min(sa, ta) + min(sb, tb) << endl;

	return 0;
}