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

// #define int long long

#define GET_MACRO(a, b, c, d, NAME, ...) NAME
#define REP2(i, n) REP3(i, 0, n)
#define REP3(i, a, b) REP4(i, a, b, 1)
#define REP4(i, a, b, s) for (ll i = (a); i < (ll)(b); i += s)
#define RREP2(i, n) RREP3(i, 0, n)
#define RREP3(i, a, b) for (ll i = (b) - 1; i >= (ll)(a); i--)

#define rep(...) GET_MACRO(__VA_ARGS__, REP4, REP3, REP2)(__VA_ARGS__)
#define rrep(...) GET_MACRO(__VA_ARGS__,, RREP3, RREP2)(__VA_ARGS__)
#define eb emplace_back
#define ef emplace_front
#define pb pop_back
#define pf pop_front
#define all(c) begin(c), end(c)
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define popcnt __builtin_popcountll

using uint = unsigned;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;

template<typename T>
using maxheap = priority_queue<T, vector<T>, less<T>>;

template<typename T>
using minheap = priority_queue<T, vector<T>, greater<T>>;

const int INF = 1e9 + 10;
const ll LLINF = 1e18 + 10;

const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, -1, 0, 1};
const int dx8[] = {-1, -1, 0, 1, 1, 1, 0, -1};
const int dy8[] = {0, -1, -1, -1, 0, 1, 1, 1};

template<typename T>
inline T sq(T x){
	return x * x;
}

template<typename T, typename U>
inline bool chmax(T &x, U y){
	if (x >= y) return false;
	x = y;
	return true;
}

template<typename T, typename U>
inline bool chmin(T &x, U y){
	if (x <= y) return false;
	x = y;
	return true;
}

template<typename T>
inline T& sort(T &c){
	sort(all(c));
	return c;
}

template<typename T>
inline T& reverse(T &c){
	reverse(all(c));
	return c;
}

template<typename T>
inline T& unique(T &c){
	sort(all(c));
	c.erase(unique(all(c)), end(c));
	return c;
}

template<typename T>
inline T sorted(const T &c){
	T d = c;
	return sort(d);
}

template<typename T>
inline T reversed(const T &c){
	T d = c;
	return reverse(d);
}

template<typename T>
inline T uniqued(const T &c){
	T d = c;
	return unique(d);
}

template<typename T>
T power(T x, long long r, const T &e = 1){
	T res(e);
	while (r){
		if (r & 1) res = res * x;
		x = x * x;
		r >>= 1;
	}
	return res;
}
// }}}

int main()
{
	int d;
	string s, t;
	cin >> d >> s >> t;
	s = "xxxxxxxxxxxxxx" + s + t + "xxxxxxxxxxxxxx";
	int res = 0;
	rep(i, 29){
		t = s;
		rep(j, i, i + d){
			if (t[j] == 'o') break;
			t[j] = 'o';
		}
		int ct = 0;
		for (auto c : t){
			if (c == 'o') chmax(res, ++ct);
			else ct = 0;
		}
	}
	cout << res << endl;
}