#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int getlen(string w) {
    int ret = 0;
    int temp = 0;
    for(char c: w) {
        if(c == 'o') {
            temp += 1;
        } else {
            temp = 0;
        }
        ret = max(ret, temp);
    }
    return ret;
}

int main() {
    int d;
    string s1,s2;
    string base = "xxxxxxxxxxxxxx";
    cin >> d;
    cin >> s1 >> s2;
    base += s1;
    base += s2;
    base += "xxxxxxxxxxxxxx";

    int result = 0;
    rep(i, 42+1-d) {
        string temp = base;
        rep(j, d) temp[j+i] = 'o';
        result = max(result, getlen(temp));
    }

    cout << result << "\n";
}