package no204a;

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int d = sc.nextInt();
		char[] c = new char[100];
		for(int i=0;i<2;i++) {
			char[] s = sc.next().toCharArray();
			for(int j=0;j<7;j++) {
				c[20+i*7+j] = s[j];
			}
		}
		int max = 0;
		for(int k=0;k<100;k++) {
			int now = 0;
			int yukyuu = 0;
			for(int i=0;i<100;i++) {
				if (i == k) {
					yukyuu = d;
				}
				if (c[i] == 'o') {
					now++;
					max = Math.max(max, now);
					yukyuu = 0;
				}else if(yukyuu > 0){
					now++;
					max = Math.max(max, now);
					yukyuu--;
				}else{
					now = 0;
				}
			}
		}
		System.out.println(max);
	}
}