#include<stdio.h>
int main()
{
	int n, m;
	scanf("%d %d", &n, &m);
	char s[10004], t[10004];
	scanf("%s%s", s, t);
	int sa, sb, ta, tb;
	sa = sb = ta = tb = 0;
	int i;
	for (i = 0; i < n; i++)
	{
		if (s[i] == 'A')
			sa++;
		else
			sb++;
	}
	for (i = 0; i < m; i++)
	{
		if (t[i] == 'A')
			ta++;
		else
			tb++;
	}
	int ans = 0;
	if (sa < ta)
		ans += sa;
	else
		ans += ta;
	if (sb < tb)
		ans += sb;
	else
		ans += tb;
	printf("%d\n", ans);
	return 0;
}