#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>

using namespace std;

int calc(string gw, int idx, int d) {
	int holidays = 0;
	int max_holidays = 0;

	bool paid = (gw[idx] == 'x');

	for (int i = 0; i < gw.size(); i++) {
		if (gw[i] == 'o' || (paid && idx <= i && i < idx + d)) {
			holidays++;
		} else {
			if (i >= idx) {
				paid = false;
			}
			max_holidays = max(max_holidays, holidays);
			holidays = 0;
		}
	}
	max_holidays = max(max_holidays, holidays);
	return max_holidays;
}

int main() {
	string in1, in2;
	int d;

	cin >> d >> in1 >> in2;
	string gw = in1 + in2;

	int ans = 0;

	for (int i = 0; i < gw.size(); i++) {
		ans = max(ans, calc(gw, i, d));
	}

	cout << ans << endl;
	return 0;
}