#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int n, m;
string s;
string t;
int cntS[2], cntT[2];

int main() {
	int i;
	
	cin >> n >> m >> s >> t;
	
	for (i = 0; i < s.length(); i++) cntS[s[i] - 'A']++;
	for (i = 0; i < t.length(); i++) cntT[t[i] - 'A']++;
	
	cout << min(cntS[0], cntT[0]) + min(cntS[1], cntT[1]) << endl;
	return 0;
}