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

class Program
{
    static string InputPattern = "Input4";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("2");
            WillReturn.Add("oxxoxxo");
            WillReturn.Add("ooooxxo");
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("5");
            WillReturn.Add("ooxxxxx");
            WillReturn.Add("ooooooo");
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("1");
            WillReturn.Add("oxxxxxo");
            WillReturn.Add("xoxxxxo");
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int D = int.Parse(InputList[0]);
        string DayStr = InputList[1] + InputList[2];

        //前後に有給休暇の数分の平日を付加
        DayStr = new string('x', D) + DayStr + new string('x', D);
        int UB = DayStr.Length - 1;

        var AnswerKouhoList = new List<string>();
        for (int I = 0; I <= UB; I++) {
            //現在の添字から連続したD日分の平日があったら、解の候補
            if (I + D - 1 > UB) break;

            string wkSubStr = DayStr.Substring(I, D);
            if (wkSubStr.Contains('o')) continue;

            var wkCharList = new List<char>();
            for (int J = 0; J <= UB; J++) {
                if (I <= J && J <= I + D - 1) wkCharList.Add('o');
                else wkCharList.Add(DayStr[J]);
            }

            AnswerKouhoList.Add(new string(wkCharList.ToArray()));
        }
        //AnswerKouhoList.ForEach(X => Console.WriteLine(X));
        Console.WriteLine(AnswerKouhoList.Max(X => DeriveMaxSeqCnt(X)));
    }

    //String型を引数として、最大のoの連続数を返す
    static int DeriveMaxSeqCnt(string pDayStr)
    {
        int MaxSeqCnt = 0;
        int CurrSeqCnt = 0;

        foreach (char EachChar in pDayStr) {
            if (EachChar == 'o') CurrSeqCnt++; //休日だった場合
            else CurrSeqCnt = 0;//平日だった場合

            if (MaxSeqCnt < CurrSeqCnt)
                MaxSeqCnt = CurrSeqCnt;
        }
        return MaxSeqCnt;
    }
}