using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace foryuki
{
    class Program
    {
        static void Main(string[] args)
        {
            int D = int.Parse(Console.ReadLine());
            string str = "";
            for (int i = 0; i < D; i++)
            {
                str += "x";
            }
            str += Console.ReadLine() + Console.ReadLine();
            for (int i = 0; i < D + 1; i++)
            {
                str += "x";
            }
            char[] C = str.ToCharArray();

            //----------------------------------

            int max = 0;
            int cnt;

            int j;
            int q;
            for (int i = 0; i < C.Length - D; i++)
            {
                q = D;
                cnt = 0;

                j = i;
                while (C[j] == 'o')
                {
                    cnt++;
                    j++;
                }

                //------

                while (C[j] == 'x' &&  q > 0)
                {
                    q--;
                    cnt++;
                    j++;
                }


                //-------

                while (C[j] == 'o')
                {
                    cnt++;
                    j++;
                }

                max = Math.Max(max, cnt);
            }


            Console.WriteLine(max);
        }


        //-------------------------------------------------------------

        static int[] ConvertStringArrayToIntArray(string[] str)
        {
            int[] b = Array.ConvertAll<string, int>(str, delegate(string value)
                {
                    return int.Parse(value);
                });
            return b;
        }

        static List<int> ConvertStringArrayToIntList(string[] str)
        {
            var list = new List<int>();
            foreach (var c in str)
            {
                list.Add(int.Parse(c));
            }
            return list;
        }
    }
}