#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>
#include<limits>

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ll, string> pls;

int main()
{
	int D,ans = 0;  cin >> D;
	string c1, c2,c3,c_temp;  cin >> c1 >> c2;
	c3 = "xxxxxxxxxxxxxx";
	c1 =c3 + c1 + c2 + c3;
	c_temp = c1;

	for (int i = 0; i < c1.size(); i++) {
		int cnt = 0, cnt_mx = 0;
		c1 = c_temp;
		if (c1[i] == 'x') {
			for (int j = 0; j < D; j++) {
				if (i + j < c1.size()) {
					if (c1[i + j] != 'x')break;
					c1[i + j] = 'o';
				}
			}

			for (int j = 0; j < c1.size(); j++) {
				if (c1[j] != 'x') cnt++;
				else cnt = 0;
				
				cnt_mx = max(cnt_mx, cnt);
			}
		}
		ans = max(ans,cnt_mx);
	}
	cout << ans << endl;
	return 0;
}