#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	string r = "xxxxxxxxxxxxxxxx";
	int d;
	cin >> d;
	string s;
	for (int i = 0; i < 2; i++) {
		string t;
		cin >> t;
		s += t;
	}
	s = r + s + r;
	int len = (int) s.length();
	int ans = 0;
	for (int i = 0; i <= len - d; i++) {
		int cnt = 0;
		int t = 0;
		for (int j = 0; j < d; j++) {
			if (t == 0 && s[i + j] == 'x') t++;
			if (t == 1 && s[i + j] == 'o') t++;
			if (t == 2 && s[i + j] == 'x') t++;
		}
		if(t == 3) continue;
		for (int j = 0; j < len; j++) {
			if(i <= j && j < i + d) cnt++;
			else {
				if(s[j] == 'o') cnt++;
				else cnt = 0;
			}
			ans = max(ans, cnt);
		}
	}
	cout << ans << endl;
	return 0;
}