#include <bits/stdc++.h>
using namespace std;

int main(void){
	string s1,s2;
	int d;
	cin >> d;
	cin >> s1 >> s2;
	s1 += s2;
	s1 ="xxxxxxxxxxxxxx" + s1 + "xxxxxxxxxxxxxx";
	string s = s1;
	int ret = 0;
	for(int i=0;i<s.size();i++){
		s = s1;
		for(int j=0;j<d&&i+j<s.size();j++){
			if(s[i+j] == 'o')break;
			s[i+j] = 'o';
		}
		int a = 0;
		for(int j=0;j<s.size();j++){
			if(s[j] == 'o')a++;
			else a = 0;
			ret = max(ret,a);
		}
	}
	cout << ret << endl;
	return 0;
}