#include<iostream>
#include<string>
using namespace std;
int main(){
	int d;
	string s, t;
	cin >> d >> s >> t;
	s =  "xxxxxxxxxxxxxx"+s + t+"xxxxxxxxxxxxxx" ;
	string sr = s;
	int ans = 0;
	for (int i = 0; i < sr.size(); i++){
		sr = s;
		for (int j = 0; j < d && i + j < sr.size(); j++){
			if (sr[i + j] == 'o') break;
			sr[i + j] = 'o';
		}
		int cnt = 0;
		for (int j = 0; j < s.size(); j++){
			if (sr[j] == 'o')cnt++;
			else cnt = 0;
			if (cnt > ans) ans = cnt;
		}
	}
	cout << ans << endl;
	return 0;
}