#include<bits/stdc++.h>
using namespace std;
int f(string str){
    int ma=0;
    int cur=0;
    while(cur<str.size()){
        int cnt=0;
        while(cur<str.size()&&str[cur]=='o')cur++,cnt++;
        ma=max(ma,cnt);
        while(cur<str.size()&&str[cur]=='x')cur++;
    }
    return ma;
}

int main(){
    int D;
    string str;
    cin>>D;
    for(int i=0;i<2;i++){
        string s;cin>>s;str+=s;
    }
    str="xxxxxxxxxxxxxx"+str+"xxxxxxxxxxxxxx";
    int ans=0;

    for(int i=0;i<str.size();i++){
        string s=str;
        for(int j=0;j<D&&i+j<s.size()&&s[i+j]=='x';j++)s[i+j]='o';
        ans=max(ans,f(s));
    }
    cout<<ans<<endl;
}