#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000000000
	

int main(){	
	int D;
	cin>>D;
	string s,t;
	cin>>s>>t;
	s += t;
	
	rep(_,14)s.insert(s.begin(),'x');
	rep(_,14)s.push_back('x');
	
	int ans = 0;
	rep(k,s.size()){
		t = s;
		rep(l,s.size()){
			t = s;
			rep(m,D){
				if(l+m<t.size())t[l+m] = 'o';
			}
			rep(i,s.size()){
				for(int j=1;j<=s.size();j++){
					if(t.substr(i,j)==string(j,'o'))ans = max(ans,j);
				}
			}
		}
	}
	
	cout<<ans<<endl;
	
	return 0;
	
}