#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
using namespace std;


int main()
{
    int n, m, ans;
    cin >> n >> m;
    vector<int> up(2, 0), down(2, 0);
    string s, t;
    cin >> s >> t;
    for (int i = 0; i < s.size(); i++){
        if (s[i] == 'A') up[0]++;
        else up[1]++;
    }
    for (int i = 0; i < t.size(); i++){
        if(t[i] == 'A') down[0]++;
        else down[1]++;
    }
    cout << min(up[0], down[0]) + min(up[1], down[1]) << endl;
}