using System.Collections.Generic;
using System.Linq;
using System;

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        var t = new string('x', n);
        var t2 = new string('o', n);
        var s = t + Console.ReadLine().Trim() + Console.ReadLine().Trim() + t;
        var p = 0;
        var ans = new List<int>();
        while (p <= s.Length - n)
        {
            var a = s.IndexOf(t, p);
            if (p >= 0)
            {
                var a2 = s.Substring(0, a) + t2 + s.Substring(a + n);
                ans.Add(countO(a2));
                p++;
            }
            else break;
        }
        Console.WriteLine(ans.Max());
    }
    public static int countO(string s)
    {
        var ans = 0;
        var count = 0;
        var cbegin = false;
        foreach (var x in s)
            if (x == 'o')
            {
                count++;
                if (cbegin) ans = Math.Max(ans, count);
                else cbegin = true;
            }
            else
            {
                count = 0;
                cbegin = false;
            }
        return ans;
    }
}