#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

template<typename T>
vector<pair<T,int> > runLength(const T a[], int n) {
	vector<pair<T,int> > r;
	if(n <= 0) return r;
	int cnt = 0;
	for(int i = 0; i <= n; i ++) {
		if(i == n || (i != 0 && a[i] != a[i-1])) {
			r.push_back(make_pair(a[i-1], cnt));
			cnt = 0;
		}
		cnt ++;
	}
	return r;
}

int main() {
	int D;
	while(cin >> D) {
		string s, t;
		cin >> s >> t;
		string x = string(14,'x') + s + t + string(14,'x');
		int ans = 0;
		string u;
		rer(d,0,D)rer(i, 0, (int)x.size()-d) {
			bool ok = true;
			u = x;
			rep(j, d) {
				ok &= u[i+j] == 'x';
				u[i+j] = 'o';
			}
			if(!ok) continue;
			auto v = runLength(&u[0], u.size());
	
			each(i, v) if(i->first == 'o')
				amax(ans, i->second);
	
		}
		cout << ans << endl;
	}
	return 0;
}