#define _CRT_SECURE_NO_WARNINGS
//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
//#define int ll
//#define endl "\n"
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
template<class T> ostream & operator<<(ostream & os, vector<T> const &);
template<int n, class...T> typename enable_if<(n>=sizeof...(T))>::type _ot(ostream &, tuple<T...> const &){}
template<int n, class...T> typename enable_if<(n< sizeof...(T))>::type _ot(ostream & os, tuple<T...> const & t){ os << (n==0?"":" ") << get<n>(t); _ot<n+1>(os, t); }
template<class...T> ostream & operator<<(ostream & os, tuple<T...> const & t){ _ot<0>(os, t); return os; }
template<class T, class U> ostream & operator<<(ostream & os, pair<T,U> const & p){ return os << "(" << p.first << ", " << p.second << ") "; }
template<class T> ostream & operator<<(ostream & os, vector<T> const & v){ rep(i,v.size()) os << v[i] << (i+1==(int)v.size()?"":" "); return os; }
template<class T> inline bool chmax(T & x, T const & y){ return x<y ? x=y,true : false; }
template<class T> inline bool chmin(T & x, T const & y){ return x>y ? x=y,true : false; }
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<mt(__VA_ARGS__)<<" ["<<__LINE__<<"]"<<endl)
#else
#define dump(...)
#endif
// ll const mod = 1000000007;
// ll const inf = 1LL<<60;

int solve(string const & s){
    int res = 0;
    int cur = 0;
    rep(i,s.size()){
        if(s[i]=='o') cur++;
        else cur = 0;
        res = max(res, cur);
    }
    return res;
}

signed main(){
    int D_;
    while(cin >> D_){
        string s,s_;
        cin >> s >> s_;
        s = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" + s + s_ + "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
        int N = s.size();
        int ans = 0;
        for(int D = 0; D <= D_; D++){
            rep(i,N-D+1){
                bool ok = true;
                rep(j,D) ok &= s[i+j] == 'x';
                if(ok){
                    string t = s;
                    rep(j,D) t[i+j] = 'o';
                    ans = max(ans, solve(t));
                }
            }
        }
        cout << ans << endl;
    }
}