#include <iostream>
#include <string>

constexpr int N = 42;

void solve() {
    int d;
    std::cin >> d;

    std::string s;
    s += std::string(14, 'x');

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

    s += std::string(14, 'x');

    int ans = 0;
    for (int si = 0; si < N; ++si) {
        int cont = 0, max = 0;
        bool valid = true;

        for (int i = 0; i < N; ++i) {
            if (s[i] == 'o' && (si <= i && i < si + d)) valid = false;
            if (s[i] == 'o' || (si <= i && i < si + d)) {
                ++cont;
            } else {
                cont = 0;
            }
            max = std::max(max, cont);
        }

        if (valid) ans = std::max(ans, max);
    }

    std::cout << ans << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}