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

int main(){
	int d;
	cin >> d;
	string c1,c2;
	cin >> c1 >> c2;
	c1 = "xxxxxxxxxxxxxx" + c1 + c2 + "xxxxxxxxxxxxxx";
	int ans = 0;
	for(int i = 0; i < c1.size() - ans; i++){
		int count = 0, check = 0;
		bool flag = false;
		for(int j = i; j < c1.size(); j++){
			if(c1[j] == 'o' and check > 0) flag = true;
			if(c1[j] == 'x'){
				if(check == d or flag) break;
				check++;
			}
			count++;
		}
		ans = max(count,ans);
	}
	cout << ans << endl;
	return 0;
}