import java.util.Scanner;
public class Yuki204{
	public static void main(String[] arg){
		Scanner sc = new Scanner(System.in);
		int d,res = 0;
		String[] week0 = new String[2];
		String week;
		int[] hol = new int[14];
		boolean use = false;
		d = sc.nextInt();
		week0[0] = sc.next();
		week0[1] = sc.next();
		week = week0[0] + week0[1];
		for(int i = 0;i<14;i++){
			int h = 0;
			for(int j = 0;j<14-i;j++){
				if(week.charAt(i+j)=='o'){
					h++;
				}else{
					if(use == false){
						h += d;
						j += d-1;
						use = true;
					}else{
						break;
					}
				}
			}
			hol[i] = h;
			use = false;
		}
		for(int i = 0;i<14;i++){
			if(hol[i]>res)res = hol[i];
		}
		System.out.println(res);
	}
}