#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<int, int> P;


const string weekly = "xxxxxxx";
int cnt[50];

int max_holiday (string s ){
	memset (cnt, 0, sizeof (cnt ) );
	cnt[0] = (s[0] == 'o' );
	int n = s.length();

	for (int i = 1; i < n; i++ ){
		if (s[i] == 'o' )
			cnt[i] = cnt[i-1] + 1;
		else
			cnt[i] = 0;
	} // end for

	int res = 0;
	rep (i, n ) res = max (res, cnt[i] );

	return res;
}

/*
	OK!
	xxxxooooxxxx
	--oooooo----

	NG!
	xxxxooooxxxx
	---oooooo---

	OK!
	ooooxxxxoooo
	---oooooo---

	NG!
	xxxxooooxoxx
	---ooooooo--

	×が連続している部分は OK。
	×が離れて存在する部分は NG。
			
*/


string replace (string s, string t, int p ){

	string u = "";
	u = s;
	rep (i, t.length() ){
		if (u[p+i] == 'o' ) break;
		u[p+i] = t[i];
	} // end rep

	return u;   
}	

int main()
{
	ios_base::sync_with_stdio(0);
	int D; cin >> D;
	string c1; cin >> c1;
	string c2; cin >> c2;
	string s = "";
	rep (i, 2 ) s += weekly;
	s += c1; s += c2;
 	rep (i, 2 ) s += weekly;

	string t = "";
	rep (i, D ) t += 'o';

	int res = 0;
	rep (i, s.length() - t.length() + 1 ){
		string u = replace (s, t, i );
		int curr = max_holiday (u );
		res = max (res, curr );
	} // end rep
//	cerr << D << ' ' << s << endl;
	cout << res << endl;

	return 0;
}