#include "bits/stdc++.h"
using namespace std;
#define fastcin {\
    cin.tie(0);\
    ios::sync_with_stdio(false);\
}
#define rep(i, a, b) for(int i = a; i < b; i++)
#define print(x) cout << x << "\n"

int main() {
    fastcin;
    int n, m;
    cin >> n >> m;
    string s, t;
    cin >> s >> t;
    int ans = min(count(s.begin(), s.end(), 'A'), count(t.begin(), t.end(), 'A')) + min(count(s.begin(), s.end(), 'B'), count(t.begin(), t.end(), 'B'));
    print(ans);
    return 0;
}