#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <iomanip>
#include <array>
#include <numeric>
#include <regex>
#include <bitset>
#include <deque>

using namespace std;
typedef long long ll;
typedef pair<int, int> p_ii;

const int INF = 1e9;
const double PI = acos(-1.0);
const ll MOD = 1e9 + 7;



int main() {
    int d; cin>>d;
    string p,s,t;
    cin>>p;
    cin>>s;
    t="xxxxxxxxxxxx";
    p=t+p+s+t;
    
    int cnt=0, res=0;
    for (int i = 0; i < 42; i++) {
        string tmp=p;
        for (int j = 0; j < d; j++) {
            if(tmp[i+j]=='o')break;
            tmp[i+j]='o';
        }
        cnt=0;
        for (int j = 0; j < 42; j++) {
            if(tmp[j]=='x'){
                res=max(res,cnt);
                cnt=0;
            }
            else if(tmp[j]=='o')cnt++;
        }
        res=max(res,cnt);
        
    }
    cout<<res<<endl;    

    return 0;
}