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

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		bool[] isPrime = new bool[M+1];
		for(int i=2;i<=M;i++) isPrime[i] = true;
		List<int> P = new List<int>();
		for(int i=2;i<=M;i++){
			if(!isPrime[i])continue;
			P.Add(i);
			for(int j=i+i;j<=M;j+=i) isPrime[j] = false;
		}
		
		int[] dp = new int[M+1];
		for(int i=0;i<=M;i++) dp[i] = -1;
		dp[0] = 0;
		foreach(var p in P){
			for(int i=M;i>=0;i--){
				if(dp[i] == -1) continue;
				if(i+p <= M){
					dp[i+p] = Math.Max(dp[i+p],dp[i]+1);
				}
			}
		}
		
		Console.WriteLine(dp[M]);
		
		
		
	}
	int M;
	public Sol(){
		M = ri();
	}

	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(char sep=' '){return Console.ReadLine().Split(sep);}
	static int[] ria(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>int.Parse(e));}
	static long[] rla(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>long.Parse(e));}
	static double[] rda(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>double.Parse(e));}
}