using System;
using System.Collections.Generic;
using System.Linq;
using static Input;

public class Prog
{
    public struct Pair { public int x, y; public Pair(int x, int y) { this.x = x; this.y = y; } }
    public static void Solve()
    {
        int N = NextInt();
        bool[] memo = Enumerable.Repeat(true, N + 1).ToArray();
        List<int> fact = new List<int>();
        for (int x = 2; x <= N; x++)
        {
            if (memo[x]) fact.Add(x);
            else continue;
            for (int t = 2; t * x <= N; t++) memo[t * x] = false;
        }
        int[] dp = Enumerable.Repeat(-INF, N + 1).ToArray();
        dp[0] = 0;
        foreach (var e in fact)
            for (int x = N - e; x >= 0; x--) dp[x + e] = Math.Max(dp[x + e], dp[x] + 1);
        Console.WriteLine(dp[N] > 0 ? dp[N] : -1);
    }
    public static void Main()
    {
        var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);
        Solve();
        Console.Out.Flush();
    }
}
public class Input
{
    public const long MOD = 1000000007;
    public const int INF = 1000000007;
    private static Queue<string> q = new Queue<string>();
    private static void Confirm() { if (q.Count == 0) foreach (var s in Console.ReadLine().Split(' ')) q.Enqueue(s); }
    public static int NextInt() { Confirm(); return int.Parse(q.Dequeue()); }
    public static long NextLong() { Confirm(); return long.Parse(q.Dequeue()); }
    public static string NextString() { Confirm(); return q.Dequeue(); }
    public static double NextDouble() { Confirm(); return double.Parse(q.Dequeue()); }
    public static int[] LineInt() { return Console.ReadLine().Split(' ').Select(int.Parse).ToArray(); }
    public static long[] LineLong() { return Console.ReadLine().Split(' ').Select(long.Parse).ToArray(); }
    public static string[] LineString() { return Console.ReadLine().Split(' ').ToArray(); }
    public static double[] LineDouble() { return Console.ReadLine().Split(' ').Select(double.Parse).ToArray(); }
    public long Abs(long a, long b) => Math.Abs(a - b);
}