#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <cstring>
#include <queue>
#include <stack>
#include <functional>
#include <math.h>
#include <iomanip>
using namespace std;
#define Would
#define you
const int INF = 999999999;
const int MOD = 1e9 + 7;
const double pi = 3.141592653589793238;

int main() {
	int a, b, ans = 0;
	string s, h;
	cin >> a >> b >> s >> h;
	sort(s.begin(), s.end()), sort(h.begin(), h.end());
	cout << min(s.find('A' - '0'), s.find('B' - '0')) + min(h.find('A' - '0'), h.find('B' - '0')) << endl;
}