import java.util.Scanner;

public class Main {
    public static void main(String[] argv) {
        Scanner scanner = new Scanner(System.in);
        int d = scanner.nextInt();
        String s = scanner.next();
        s += scanner.next();
        s = "xxxxxxxxxxxxxx" + s + "xxxxxxxxxxxxxx";
        int res = 0;
        for (int i = 0; i < 42; ++i) {
            int len = 0;
            for (int j = 0; j < d && j < 42 - i; ++j) {
                if (s.charAt(i + j) == 'o') {
                    break;
                }
                len++;
            }
            int count = 0;
            for (int j = 0; j < 42; ++j) {
                boolean isYukyu = (j >= i) && ((j - i) < len);
//                boolean isYukyu = (j >= i) && ((j - i) < d);
                if (s.charAt(j) == 'o' || isYukyu) {
                    count++;
                    res = Math.max(res, count);
                } else {
                    count = 0;
                }
            }
        }
        System.out.println(res);
    }
}