import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int d = Integer.parseInt(br.readLine());
        char[] arr = new char[14];
        for (int i = 0; i < 2; i++) {
            char[] line = br.readLine().toCharArray();
            for (int j = 0; j < 7; j++) {
                arr[i * 7 + j] = line[j];
            }
        }
        int max = 0;
        for (int i = 0; i < 14; i++) {
            boolean norm = false;
            boolean hor = false;
            int count = 0;
            int dCount = 0;
            for (int j = i; j < 14; j++) {
                if (arr[j] == 'o') {
                    if (norm) {
                        hor = true;
                    }
                } else {
                    if (hor) {
                        break;
                    } else {
                        norm = true;
                    }
                    dCount++;
                    if (dCount > d) {
                        break;
                    }
                }
                count++;
            }
            max = Math.max(max, count);
        }
        System.out.println(max);
    }
}