#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include<iomanip>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(int i = m;i >= n;--i)
#define INF INT_MAX/2
using namespace std;
using ll = long long;
using R = double;
using Data = pair<ll, vector<int>>;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 50;
struct edge { ll from; ll to; ll cost; };

int check(int msk) {
	int pre = msk % 2;
	msk /= 2;
	int ok = 1;
	while (msk > 0) {
		int temp = msk % 2;
		
		if (temp == 1) {
			if (!ok)return false;
		}
		else {
			if (pre == 1)ok = 0;
		}

		pre = temp;
		msk /= 2;
	}
	return true;
}


int main() {
	int d;
	cin >> d;
	string date = "";
	rep(i, 0, 2) {
		string s;
		cin >> s;
		date += s;
	}


	int ans = -101010;
	rep(msk, 0, (1 << 14)) {
		string temp = date;
		int cnt = 0;
		rep(i, 0, 14) {
			if ((1 << i)&msk && date[i] == 'x') {
				temp[i] = 'o';
				cnt++;
			}
		}

		if (cnt != d || !check(msk))continue;
		int seq = 0;
		rep(i, 0, 14) {
			if (temp[i] == 'o')seq++;
			else seq = 0;
			ans = max(seq, ans);
		}
	}
	cout << ans << endl;



	return 0;
}