#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    int d;
    string s,t;
    cin>>d>>s>>t;
    s+=t;
    s="xxxxxxxxxxxxxx"+s+"xxxxxxxxxxxxxx";
    int n=s.size();
    int mx=0;
    for (int i=0;i<n;i++) {
        int k=0;
        for (int j=0;j<n;j++) {
            if (d!=0&&j==i&&s[j]=='x') {
                while (j<n&&j<i+d&&s[j]=='x') {
                    k++;
                    j++;
                }
                j--;
            } else if (s[j]=='o') {
                k++;
            } else {
                k=0;
            }
            mx=max(mx,k);
        }
    }
    cout<<mx<<endl;
    return 0;
}