#include <iostream>
using namespace std;

const int INF = (1 << 28);

int main() {
    int N, M;
    cin >> N >> M;

    string S, T;
    cin >> S >> T;

    int aCount = 0,
        bCount = 0;
    for (char c : S) {
        if (c == 'A') aCount++;
        else bCount++;
    }

    int ans = aCount + bCount;

    for (char c : T) {
        if (c == 'A') aCount = max(aCount - 1, 0);
        else bCount = max(bCount - 1, 0);
    }

    ans -= aCount + bCount;

    cout << ans << endl;

    return 0;
}