#include <bits/stdc++.h>

using ll = long long;

using namespace std;

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

    int n, m;
    cin >> n >> m;
    string s,t;
    cin >> s >> t;
    
    int a1{0},a2{0};
    for(const auto& it:s)
        if (it=='A') ++a1;
    for(const auto& it:t)
        if (it=='A') ++a2;
    
    cout << min(a1,a2) + min(n-a1,m-a2) << "\n";
    
    return 0;
}