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

class Program
{
    static string InputPattern = "Input3";

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

        if (InputPattern == "Input1") {
            WillReturn.Add("5");
            WillReturn.Add("1 2 3 1 2");
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("5");
            WillReturn.Add("1 2 3 4 5");
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("5");
            WillReturn.Add("1 1 1 1 1");
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        //int[] AArr = InputList[1].Split(' ').Select(X => int.Parse(X)).ToArray();
        int[] AArr = Enumerable.Range(1, 40000).ToArray();

        int UB = AArr.GetUpperBound(0);

        int Answer = 0;

        int L = 0;
        for (int R = 0; R <= UB; R++) {
            int CurrVal = AArr[R];

            //再登場の数値の場合は、左からその数値までRemoveしつつ、Lを移動
            int wkInd = Array.FindIndex(AArr, L, R - L, X => X == CurrVal);
            if (wkInd >= 0) {
                L = wkInd + 1;

                //下限値枝切り
                int RestMaxCnt = UB - L + 1;
                if (RestMaxCnt <= Answer) break;
            }

            if (Answer < R - L + 1)
                Answer = R - L + 1;
        }
        Console.WriteLine(Answer);
    }
}