package yukicoder150508;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int d = sc.nextInt();
		String c = "xxxxxxx" + "xxxxxxx" + sc.next() + sc.next() + "xxxxxxx" + "xxxxxxx";
		StringBuffer[] cc = new StringBuffer[c.length()];

		for (int i = 0; i < c.length(); i++) {
			cc[i] = new StringBuffer(c);
			for (int j = i; j < i + d && j < cc[i].length(); j++) {
				if (cc[i].charAt(j) == 'x') {
					cc[i].setCharAt(j, 'o');
				} else {
					break;
				}
			}
		}
		
		int max = 0;
		for (int j = 0; j < cc.length; j++) {
			int count = 0;
			for (int i = 0; i < cc[j].length(); i++) {
				if (cc[j].charAt(i) == 'o') {
					count++;
					max = Math.max(max, count);
				} else {
					count = 0;
				}
			}
		}

		System.out.println(max);

		sc.close();
	}
}