using System;
using System.Linq;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Text;
 
public class Program
{
    public void Proc() {
        Reader.IsDebug = false;
        this.Num = int.Parse(Reader.ReadLine());
        this.InitPrimeList(this.Num);
        this.memo = new Nullable<int>[this.PrimeList.Length, this.Num+1];
        int ans = this.GetAns(0, this.Num);
        Console.WriteLine(ans);
    }

    private Nullable<int>[,] memo;

    private int GetAns(int idx, int remain) {
        if(idx >= this.PrimeList.Length) {
            if(remain == 0) {
                return 0;
            } else {
                return -1;
            }
        }
        if(remain == 0) {
            return 0;
        }
        if(remain < 2) {
            return -1;
        }
        if(this.memo[idx, remain] != null) {
            return this.memo[idx, remain].Value;
        }
        int ans = -1;
        if(PrimeList[idx] <= remain) {
            int ret = this.GetAns(idx+1, remain-PrimeList[idx]);
            if(ret >= 0) {
                ret++;
                ans = Math.Max(ans, ret);
            }
            ret = this.GetAns(idx+1, remain);
            if(ret >= 0) {
                ans = Math.Max(ans, ret);
            }
        } else {
            int ret = this.GetAns(idx+1, remain);
            if(ret >= 0) {
                ans = Math.Max(ans, ret);
            }
        }
        this.memo[idx, remain] = ans;
        return ans;
    }
    private int[] PrimeList;

    private void InitPrimeList(int num) {
        bool[] flags = new bool[num+1];
        List<int> list = new List<int>();
        for(int i=2; i<=num; i++) {
            if(flags[i]) {
                continue;
            }
            list.Add(i);
            for(int j=1; j*i<=num; j++) {
                flags[i*j] = true;
            }
        }
        list.Reverse();
        this.PrimeList = list.ToArray();
    }

    private int Num;


    public class Reader {
        public static bool IsDebug = true;
        private static System.IO.StringReader SReader;
        private static string InitText = @"


20000



";
        public static string ReadLine() {
            if(IsDebug) {
                if(SReader == null) {
                    SReader = new System.IO.StringReader(InitText.Trim());
                }
                return SReader.ReadLine();
            } else {
                return Console.ReadLine();
            }
        }
    }
    public static void Main(string[] args)
    {
        Program prg = new Program();
        prg.Proc();
    }
}