import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;

public class Main {

	public static final int SIZE = 14;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		final int D = sc.nextInt();

		boolean[] days = new boolean[SIZE];
		for (int i = 0; i < 2; i++) {
			char[] inputs = sc.next().toCharArray();

			for (int j = 0; j < SIZE / 2; j++) {
				days[i * (SIZE / 2) + j] = inputs[j] == 'o';
			}
		}

		int max = 0;
		for (int d = 0; d <= D; d++) {
			POS:
			for (int start = 0; start <= 3 * SIZE - D; start++) {
				boolean[] new_days = new boolean[3 * SIZE];
				System.arraycopy(days, 0, new_days, SIZE, SIZE);
				
				for(int i = 0; i < d; i++){
					if(new_days[start + i]){
						continue POS;
					}
				}
				
				for (int i = 0; i < d; i++) {
					new_days[start + i] = true;
				}

				int prev = -1;
				for (int cur = 0; cur < new_days.length; cur++) {
					if (!new_days[cur] && prev >= 0) {
						max = Math.max(max, cur - prev);
						prev = -1;
					}

					if (new_days[cur] && prev < 0) {
						prev = cur;
					}
				}

				if (prev >= 0) {
					max = Math.max(max, new_days.length - prev);
				}
			}
		}

		System.out.println(max);
	}
}