#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
#define rep(i, n) for(ll (i) = 0; (i) < (n); (i)++)
#define rep1(i, n) for(ll (i) = 1; (i) <= (n); (i)++)
#define rrep(i, n) for(ll (i) = (n) - 1; (i) >= 0; (i)--)
#define rrep1(i, n) for(ll (i) = (n); (i) >= 1; (i)--)
const ll INF = 1145141919;
const ll MOD = 1000000007;
template<class T> void chmax(T &a, const T &b){if(a < b){a = b;}}
template<class T> void chmin(T &a, const T &b){if(a > b){a = b;}}

int main(){

    ll D;
    cin >> D;
    string s = "";
    rep(i, 2){
        string t;
        cin >> t;
        s += t;
    }
    rep(i, 50)s += "x";
    ll ans = 0;
    for(ll i = 0; i <= 15; i++){
        string t = s;
        if(i < 15 && t[i] == 'x'){
            rep(j, D){
                if(t[i + j] == 'o')break;
                t[i + j] = 'o';
            }
        }
        ll cnt = 0;
        rep(j, t.size()){
            if(t[j] == 'x')cnt = 0;
            else cnt++;
            chmax(ans, cnt);
        }
    }
    cout << ans << endl;

    return 0;
}