#include <iostream>

using namespace std;

int main()
{
    int D;
    string s, t;
    cin >> D;
    cin >> s; t += s;
    cin >> s; t += s;
    
    int res = 0;
    for (int i = 0; i < 14; i++) {
        int l = i, r = i + D;
        int sum = 0;
        for (int j = 0; j < 14; j++) {
            if (t[j] == 'o' || (l <= j && j < r)) {
                sum++;
            } else {
                sum = 0;
            }
            res = max(res, sum);
        }
    }
    cout << res << endl;
    return 0;
}