#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define int long long
using namespace std;
typedef pair<int, int> P;
const int INF = 1e15;


signed main(){
    int n, m;
    cin >> n >> m;
    string s, t;
    cin >> s >> t;
    int as = 0, at = 0;
    rep(i, 0, n) if(s[i] == 'A') as++;
    rep(i, 0, m) if(t[i] == 'A') at++;
    int ans = min(as, at) + min(n - as, m - at);
    cout << ans << endl;
}