#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (int)n; ++i)
#define REP(i, a, b) for (int i = (int)a; i < (int)b; ++i)
#define rer(i, a, b) for (int i = (int)a; i <= (int)b; ++i)
#define each(i,c) for(__typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define all(v) v.begin(), v.end()
#define mset(a, n) memset(a, n, sizeof(a))

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vector<int> > vvi;
typedef vector<pair<int, int> > vpii;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

const int inf = 1000000000;
const int mod = 1000000007;
const double eps = 1e-9;
const int dx[] = { -1, 0, 1, 0};
const int dy[] = { 0, -1, 0, 1};

int main() {
	// cin.tie(0); // tie
	// ios::sync_with_stdio(false); // sync
	int d;
	string s1, s2;
	cin >> d;
	cin >> s1 >> s2;
	s1 += s2;
	vector<string> vs;
	rep(i, s1.size()) {
		int d2 = d;
		string tmp = s1;
		if (tmp[i] == 'x') {
			for (int j = i; d2 > 0; --d2, ++j) {
				tmp[j] = 'o';
			}
		}
		vs.push_back(tmp);
	}

	// for (auto i : vs) cout << i << endl;

	int ans = 0;
	rep(i, vs.size()) {
		int cnt = 0;
		rep(j, vs[i].size()) {
			if (vs[i][j] == 'o') cnt++;
			else cnt = 0;
			ans = max(ans, cnt);
		}
	}
	cout << ans << endl;
	return 0;
}