#include <iostream>
#include <string>

using namespace std;

int f(string a)
{
    a += "x";

    int ma = 0;
    
    bool st = true;
    int s;
    for (int i = 0; i < a.size(); ++i) {
        if (st && a[i] == 'o') {
            s = i;
            st = false;
        } else if (!st && a[i] == 'x') {
            ma = max(ma, i - s);
            st = true;
        }
    }

    return ma;
}

int main()
{
    int d; cin >> d;
    string a = "xxxxxxxxxxxxxx";

    string s = "";
    for (int i = 0; i < 2; ++i) { string t; cin >> t; s += t; }
    s = a + s + a;

    int ma = 0;

    for (int i = 0; i < s.size() - 14; ++i) {
        string t = s;
        for (int j = 0; j < d; ++j) t[i+j] = 'o';
        ma = max(ma, f(t));
    }

    cout << ma << endl;
}