using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;


class Template
{
	static Scanner sc;
	static int D;
	static string c = "";
	public static void Main(string[] args)
	{
		sc = new Scanner();
		D = sc.nextInt();
		for (int i = 0; i < 2; i++)
		{
			c += sc.next();
		}
		int ans = 0;
		for (int i = 0; i < 14; i++)
		{
			ans = Math.Max(ans, func(i));
		}
		Console.WriteLine(ans);
	}
	static int func(int d)
	{
		int res = 0;
		string bufs = String.Copy(c);
		char[] buf = bufs.ToArray();
		for (int i = 0; i + d < buf.Length && i < D; i++)
		{
			if (buf[i + d] == 'o') break;
			buf[i + d] = 'o';
		}
		int cnt = 0;
		for (int i = 0; i < buf.Length; i++)
		{
			if (buf[i] == 'o') cnt++;
			else
			{
				res = Math.Max(res, cnt);
				cnt = 0;
			}
		}
		res = Math.Max(res, cnt);
		return res;
	}
}

public class Scanner
{
	public Scanner() { }
	public string next()
	{
		return Console.ReadLine();
	}
	public int nextInt()
	{
		return int.Parse(next());
	}
	public double nextDouble()
	{
		return double.Parse(next());
	}
	public long nextLong()
	{
		return long.Parse(next());
	}
	public string[] nextArray()
	{
		return next().Split(' ');
	}
	public int[] nextIntArray()
	{
		return Array.ConvertAll(nextArray(), e => int.Parse(e));
	}
	public long[] nextLongArray()
	{
		return Array.ConvertAll(nextArray(), e => long.Parse(e));
	}
	public double[] nextDoubleArray()
	{
		return Array.ConvertAll(nextArray(), e => double.Parse(e));
	}
}