#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define pb(a) push_back(a)
#define pr(a) cout<<(a)<<endl
#define PR(a,b) cout<<(a)<<" "<<(b)<<endl
#define R cin>>
#define F first
#define S second
#define ll long long
bool check(int n,int m,int x,int y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
typedef pair<int,int> P;

int main() {
  int d;
  cin >> d;
  string s="";
  rep(i,2) {
    string t;
    cin >> t;
    s+=t;
  }
  int ans=0;
  rep(j,s.size()) {
    string t=s;
    REP(i,j,j+d) {
      if(i>=s.size() || t[i]=='o') break;
      t[i]='o';
    }
    t+='x';
    int a=0,cnt=0;
    rep(i,t.size()) {
      if(t[i]=='o') cnt++;
      else cnt=0;
      a=max(a,cnt);
    }
    ans=max(ans,a);
  }
  cout << ans << endl;
  return 0;
}