#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 cnt(string s){
    int ans = 0;
    int cur = 1;
    for(int i=1;i<s.size();i++){
        if(s[i]=='o' && s[i]==s[i-1]) cur++;
        else cur = 1;
        ans = max(ans,cur);
    }
    return ans;
}

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    int D;
    cin >> D;
    string s,t;
    cin >> s >> t;
    s = string("xxxxxxx") + "xxxxxxx" + s + t + "xxxxxxx" + "xxxxxxx";
    int ans = 0;
    for(int i=0;i+D-1<s.size();i++){
        bool ok = true;
        string t = s;
        for(int j=0;j<D;j++){
            if(t[i+j]=='o') ok = false;
            t[i+j] = 'o';
        }
        if(!ok) continue;
        int c = cnt(t);
        ans = max(ans, c);
    }
    cout << ans<< endl;
}