#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, m;
    cin >> n >> m;

    string s, t;
    cin >> s >> t;

    int a = 0, b = 0;
    for (int i = 0; i < n; i++) {
        a += (s[i] == 'A');
    }
    for (int i = 0; i < m; i++) {
        b += (t[i] == 'A');
    }
    n -= a;
    m -= b;

    cout << min(a, b) + min(n, m) << endl;

    return 0;
}