#include "bits/stdc++.h"

using namespace std;
using ll = long long;
const double pi = acos(-1);
#define FOR(i,a,b) for (ll i=(a),__last_##i=(b);i<__last_##i;i++)
#define RFOR(i,a,b) for (ll i=(b)-1,__last_##i=(a);i>=__last_##i;i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define __GET_MACRO3(_1, _2, _3, NAME, ...) NAME
#define rep(...) __GET_MACRO3(__VA_ARGS__, FOR, REP)(__VA_ARGS__)
#define rrep(...) __GET_MACRO3(__VA_ARGS__, RFOR, RREP)(__VA_ARGS__)
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v) {
	REP(i, v.size()) { if (i)os << " "; os << v[i]; }return os;
}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v) {
	REP(i, v.size()) { if (i)os << endl; os << v[i]; }return os;
}

const ll INF = LLONG_MAX;
ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

#define int long long

inline void my_io() {

	std::ios::sync_with_stdio(false);

	std::cin.tie(0);

	cout << fixed << setprecision(16);

	//cout << setprecision(10) << scientific << ans << endl;
}

signed main() {
	ll d;
	string s, s1, s2;

	cin >> d >> s1 >> s2;

	s = s1 + s2;
	
	string s3 = "";

	REP(i, d) {
		s3 += "x";
	}

	s = s3 + s + s3;

	ll cnt, sum;
	ll ans = 0;

	REP(i, s.size()) {
		s3 = s;
		cnt = 0;
		sum = 0;
		if (s[i] == 'x') {
			while (i + cnt < s.size() && s[i + cnt] == 'x') {
				cnt++;
			}
			REP(j, min(d, cnt)) {
				s3[i + j] = 'o';
			}
			REP(j, s3.size()) {
				cnt = 0;
				while (j + cnt < s3.size() && s3[j + cnt] == 'o') {
					cnt++;
				}
				sum = max(sum, cnt);
				j += cnt;
			}
		}
		ans = max(ans, sum);
	}

	cout << ans << endl;
}