#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N,M; cin >> N >> M;
    auto f = []() {
        string s; cin >> s;
        int a = 0, b = 0;
        for(char c : s) {
            if(c == 'A') a++;
            if(c == 'B') b++;
        }
        return pair<int,int>{a, b};
    };

    auto [sa, sb] = f();
    auto [ta, tb] = f();
    cout << min(sa, ta) + min(sb, tb) << endl;
}