#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()

typedef long long ll;
typedef pair<int, int> P;

int calc(string s, int l, int D) {
    for (int i = l; i < min(l + D, (int)s.size()) && s[i] == 'x'; i++) {
        s[i] = 'o';
    }
    int ret = 0;
    int cnt = 0;
    rep(i, s.size()) {
        if (s[i] == 'o') {
            cnt++;
        } else {
            cnt = 0;
        }
        ret = max(ret, cnt);
    }
    return ret;
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int D;
    cin >> D;
    string s(20, 'x');
    rep(i, 2) {
        string t;
        cin >> t;
        s += t;
    }
    s += string(20, 'x');

    int ans = 0;
    rep(i, s.size()) {
        if (s[i] == 'x') {
            ans = max(ans, calc(s, i, D));
        }
    }
    cout << ans << endl;
}