#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <sstream>
#include <functional>
#include <map>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <list>
#include <numeric>
using namespace std;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = 1<<25;
typedef pair<int,int> P;
typedef long long ll;
typedef unsigned long long ull;


int main(){
	int D;
	string u, s, t;
	int res = 0, cnt = 0;
	cin>>D>>s>>t;
	u = s+t;
	for(int j = 0; j < u.size(); j++){
		s = u;
		for(int k = j; k < min((int)u.size(), j+D); k++){
			if(s[k]=='o') break;
			s[k] = 'o';
		}
		cnt = 0;
		for(int i = 0; i < s.size(); i++){
			if(s[i]=='o') cnt++;
			else cnt = 0;
			res = max(res, cnt);
		}
	}
	cout<<res<<endl;
	
	return 0;
}