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

int main(){
	int d;
	cin >> d;
	string c1,c2;
	cin >> c1 >> c2;
	c1 += c2;
	int count = 0, ans = 0, check = 0;
	for(int i = 0; i < 14 - ans; i++){
		ans = max(count,ans);
		count = 0,check = 0;
		for(int j = i; j < 14; j++){
			if(c1[j] == 'x'){
				if(check == d) break;
				check++,count++;
			}else count++;
		}
	}
	cout << ans << endl;
	return 0;
}