#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 <functional>
#include <chrono>

using namespace std;
#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 DEBUG(C) cerr << #C << " = " << C << endl;
using LL = long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<LL>;
using VVL = vector<VL>;
using VD = vector<double>;
using VVD = vector<VD>;
using PII = pair<int, int>;
using PDD = pair<double, double>;
using PLL = pair<LL, LL>;
using VPII = vector<PII>;
template<typename T> using VT = vector<T>;
#define ALL(a) begin((a)), end((a))
#define RALL(a) rbegin((a)), rend((a))
#define SORT(a) sort(ALL((a)))
#define RSORT(a) sort(RALL((a)))
#define REVERSE(a) reverse(ALL((a)))
#define MP make_pair
#define FORE(a, b) for (auto &&a : (b))
#define FIND(s, e) ((s).find(e) != (s).end())
#define EB emplace_back
template<typename T> inline bool chmax(T &a, T b){if (a < b){a = b;return true;}return false;}
template<typename T> inline bool chmin(T &a, T b){if (a > b){a = b;return true;}return false;}

const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;
const long double EPS = 1e-9;

int calc(string S) {
    VI v(15, 0);
    REP(i, 14) v[i] = S[i] == 'o';
    REP(i, 14) if (v[i + 1]) v[i + 1] += v[i];
    return *max_element(ALL(v));
}

int changeCalc(string S, int st, int d) {
    FOR(i, st, st + d) {
        assert(S[i] == 'x');
        S[i] = 'o';
    }
    return calc(S);
}

int main(void) {
    int D;
    cin >> D;
    string S;
    REP(i, 2) {
        string s;
        cin >> s;
        S += s;
    }
    int ans = D;
    if (S[0] == 'o') {
        int cnt = D;
        while (cnt - D < 14 && S[cnt - D] == 'o') ++cnt;
        chmax(ans, cnt);
    }
    if (S.back() == 'o') {
        int cnt = 0;
        while (S[13 - cnt] == 'o' && cnt < 14) ++cnt;
        chmax(ans, cnt + D);
    }
    chmax(ans, calc(S));
    REP(i, 14) if (S[i] == 'x') {
        int j = 0;
        while (j + i < 14 && S[j + i] == 'x' && j < D) ++j;
        chmax(ans, changeCalc(S, i, j));
    }
    cout << ans << endl;
}