#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>
#include <random>

#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define RREP(i, a) for(int (i) = (a)-1; (i) >= 0; (i)--)
#define FORR(i, a, b) for(int (i) = (a)-1; (i) >= (b); (i)--)
#define PI acos(-1.0)
#define DEBUG(C) cerr << C << endl;
#define VI vector <int>
#define VII vector <VI>
#define VL vector <LL>
#define VLL vector <VL>
#define VD vector <double>
#define VDD vector <VD>
#define PII pair <int, int>
#define PDD pair <double, double>
#define PLL pair <LL, LL>
#define VPII vector <PII>
#define ALL(a) (a).begin(), (a).end()
#define SORT(a) sort(ALL(a))
#define REVERSE(a) reverse(ALL(a))
#define MP make_pair
#define EB emplace_back
#define FORE(a, b) for (auto &&a : b)
#define FIND(s, n) (s.find(n) != s.end())

using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;

int main(void) {
    int D; cin >> D;
    string s[2];
    REP(i, 2) cin >> s[i];
    string ss = s[0] + s[1];
    int cnt = 0;
    REP(i, ss.length()) {
        if (ss[i] == 'x') cnt++;
    }
    if (cnt <= D) {
        cout << 14 << endl;
        return 0;
    }
    int ans = 0;
    REP(i, ss.length()) {
        string sbuf = ss;
        int dbuf = D;
        //cerr << dbuf << endl;
        REP(j, sbuf.length()) if (sbuf[(j + i) % sbuf.length()] == 'x') {
            sbuf[(j + i) % sbuf.length()] = 'o';
            if (--dbuf == 0) break;
        }
        int day = 0, mday = 0;
        sbuf += 'x';
        //cerr << sbuf << endl;
        REP(j, sbuf.length()) {
            if (sbuf[j] == 'o') {
                day++;
            } else {
                mday = max(day, mday);
                day = 0;
            }
        }
        //cerr << mday << endl;
        ans = max(ans, mday);
    }
    cout << ans << endl;
    return 0;
}