using System;
using System.Collections.Generic;

namespace No204_1{
    public class Program{
        public static void Main(string[] args){
            var god = int.Parse(Console.ReadLine());
            var days = string.Empty;

            days += "\0xxxxxxxxxxxxxx";
            days += Console.ReadLine();
            days += Console.ReadLine();
            days += "xxxxxxxxxxxxxx\0";

            var happyDays = new List<int>{0};
            var fuckingDays = new List<int>{0};

            var cntx = 0;
            var cnto = 0;
            foreach(var day in days){
                if(day == 'x'){
                    cntx++;
                } else if(cntx != 0){
                    fuckingDays.Add(cntx);
                    cntx = 0;
                }

                if(day == 'o'){
                    cnto++;
                } else if(cnto != 0){
                    happyDays.Add(cnto);
                    cnto = 0;
                }
            }
            happyDays.Add(0);
            fuckingDays.Add(0);

            var max = 0;
            for(var i = 0; i < fuckingDays.Count; i++){
                if(fuckingDays[i] == god) max = Math.Max(max, happyDays[i - 1] + happyDays[i]);
                if(fuckingDays[i] > god) max = Math.Max(max, Math.Max(happyDays[i - 1], happyDays[i]));
            }

            Console.WriteLine(max + god);
        }
    }
}