#include "bits/stdc++.h"
using namespace std;

int main() {
    int D;
    cin >> D;
    string s1, s2;
    cin >> s1 >> s2;
    s1 += s2;
    int ans = 0;
    for (int j = -1; j <= 14; j++)
    {
        int cnt = 0;
        if (j == -1){
            cnt = D;
        }
        for (int i = 0; i < s1.size(); i++)
        {
            if (s1[i] == 'o' || ((i - j) >= 0 && (i - j) < D)){
                cnt++;
                ans = max(cnt, ans);
            }
            else cnt = 0;
        }
        cnt += max(0, D + j - 14);
        ans = max(cnt, ans);
    }
    cout << ans << endl;
}