#include<bits/stdc++.h>
using namespace std;
using ll = long long;
template<class T> using vt = vector<T>;
template<class T> using vvt = vector<vt<T>>;
template<class T> using ttt = tuple<T,T>;
using tii = tuple<int,int>;
using tiii = tuple<int,int,int>;
using vi = vector<int>;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define pb push_back
#define mt make_tuple
#define ALL(a) (a).begin(),(a).end()
#define FST first
#define SEC second
#define DEB cerr<<"!"<<endl
#define SHOW(a,b) cerr<<(a)<<" "<<(b)<<endl
const int INF = (INT_MAX/2);
const ll LLINF = (LLONG_MAX/2);
const double eps = 1e-8;
const ll DIV =1e9+7;
//const double PI = M_PI;
inline ll pow(ll x,ll n,ll m){ll r=1;while(n>0){if((n&1)==1)r=r*x%m;x=x*x%m;n>>=1;}return r%m;}
inline ll lcm(ll d1, ll d2){return d1 / __gcd(d1, d2) * d2;}
#define chmax(a,b) a=max(a,b)

/*Coding Space*/
 int d;
 int ans = 0;
 string s;

void cou(int i,string s){
  int ret = 0;
  int dd = 0;
  while(dd < s.size()){
    if(s[dd] == 'o'){
      dd++,ret++;
      ans = max(ans,ret);
    }else{
      ret = 0;
      dd++;
    }
  }
}

void ch(int i,string s){
  rep(j,d)if(i+j < s.size()){
    if(s[i+j] == 'o') {cou(i,s); return;}
    else s[i+j] = 'o';
  }
  cou(i,s);
}

int main(){
  cin >> d;
  cin >> s; string ts; cin >> ts; s = s+ts;
  s = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" + s + "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
  rep(i,s.size()){ch(i,s);}
  cout << ans << endl;
}