#define _USE_MATH_DEFINES
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cstring>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <numeric>
#include <functional>
#include <cctype>
#include <list>
#include <limits>
#include <cassert>
#include <random>
#include <time.h>
#include <unordered_set>
//#include <boost/multiprecision/cpp_int.hpp>



using namespace std;
using Int = long long;
//using namespace boost::multiprecision;

const double EPS = 1e-10;
long long const MOD = 998244353;

long long mod_pow(long long x, long long n) {
    long long res = 1;
    for (int i = 0;i < 60; i++) {
        if (n >> i & 1) res = res * x % MOD;
        x = x * x % MOD;
    }
    return res;
}

template<typename T>
T gcd(T a, T b) {
    return b != 0 ? gcd(b, a % b) : a;
}

template<typename T>
T lcm(T a, T b) {
    return a * b / gcd(a, b);
}

void fastInput() {
    cin.tie(0);
    ios::sync_with_stdio(false);
}

int main(void) {
    int D; cin >> D;
    string s0 = "xxxxxxxxxxxxxxxxxxxx";
    string s3 = "xxxxxxxxxxxxxxxxxxxx";
    string s1, s2; cin >> s1 >> s2;
    string S = s0+s1+s2+s3;

    int ans = 0;
    for (int N = 0; N <= D; N++) {
        for (int i = 0; i < S.length(); i++) {
            string tmp;
            int cnt = 0;
            for (int j = 0; j < S.length(); j++) {
                if (i <= j && j < i+N) {
                    if (S[j] == 'o') goto END;
                    else tmp += 'o';
                } else {
                    tmp += S[j];
                }
            }
            for (int j = 0; j < tmp.length(); j++) {
                if (tmp[j] == 'o') {
                    cnt++;
                } else {
                    ans = max(ans, cnt);
                    cnt = 0;
                }
            }
            END: continue;
        }
    }
    cout << ans << endl;
}