import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int d = sc.nextInt();
        ArrayList<Integer> cal = new ArrayList<>();
        char prev = 'x';
        int count = 20;
        for (char c : (sc.next() + sc.next()).toCharArray()) {
            if (prev == c) {
                count++;
            } else {
                cal.add(count);
                count = 1;
                prev = c;
            }
        }
        if (prev == 'x') {
            cal.add(count + 20);
        } else {
            cal.add(count);
            cal.add(20);
        }
        if (cal.size() == 1) {
            System.out.println(d);
            return;
        }
        int max = d;
        for (int i = 0; i < cal.size(); i += 2) {
            if (i > 0 && i < cal.size() - 1) {
                if (d >= cal.get(i)) {
                    max = Math.max(max, cal.get(i - 1) + cal.get(i) + cal.get(i + 1));
                } else {
                    max = Math.max(max, cal.get(i - 1) + d);
                    max = Math.max(max, cal.get(i + 1) + d);
                }
            } else if (i == 0) {
                max = Math.max(max, cal.get(1) + d);
            } else {
                max = Math.max(max, cal.get(cal.size() - 2) + d);
            }
        }
        System.out.println(max);
    }
}