#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	int d;
	cin >> d;
	string s;
	for (int i = 0; i < 2; i++) {
		string t;
		cin >> t;
		s += t;
	}
	int ans = 0;
	for (int i = 0; i <= 14 - d; i++) {
		int cnt = 0;
		for (int j = 0; j < 14; j++) {
			if(j == i) {
				cnt += d;
				j += d - 1;
				continue;
			}
			if(s[j] == 'o') cnt++;
			else cnt = 0;
			ans = max(ans, cnt);
		}
	}
	cout << ans << endl;
	return 0;
}