#include <cstdio>
#include <vector>
#include <map>
#include <algorithm>
#include <cmath>
#include <iostream>
#include <string>

#define rep(i,N) for(int (i)=0;(i)<(N);(i)++)
#define MOD 1000000007

using namespace std;

int powmod(int a, int b, int p) {
	if (b == 0)return 1;
	else if (b % 2 == 0)return (powmod(a*a, b / 2, p) % p);
	else return (powmod(a, b - 1, p)*a%p);
}

int factorialmod(int a, int p) {
	if (!a)return 1;
	else return a * factorialmod(a - 1, p) % p;
}

int main(){
	int N, M,x = 0,y = 0;
	string s, t;
	scanf("%d%d", &N, &M);
	cin >> s >> t;
	rep(i, N)if (s[i] == 'A')x++;
	rep(i, M)if (t[i] == 'A')y++;
	cout << min(x, y) + min(N - x, M - y) << "\n";
	return 0;
}