#include<iostream>
#include<string>
using namespace std;
int main(void){
	int d; string str, tmp; cin >> d >> str >> tmp;
	str = "xxxxxxxxxxxxxx" + str + tmp + "xxxxxxxxxxxxxx";
	string s = str;
	int ans = 0;
	for (int i = 0; i < s.size(); i++){
		s = str;
		for (int j = 0; j < d && i+j < s.size(); j++){
			if (s[i + j] == 'o') break;
			s[i + j] = 'o';
		}
		int cnt = 0;
		for (int j = 0; j < s.size(); j++){
			((s[j] == 'o')? cnt++ : cnt = 0);
			if (cnt > ans) ans = cnt;
		}
	}
	cout << ans << endl;
	return 0;
}