#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <array>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int main()
{
    int n, m;
    string s, t;
    cin >> n >> m >> s >> t;

    int x = count(s.begin(), s.end(), 'A');
    int y = count(t.begin(), t.end(), 'A');

    int ans = min(x, y) + min(n-x, m-y);
    cout << ans << endl;

    return 0;
}