using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;
using System.Runtime.Intrinsics.Arm;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var ans = 0;
        if (n >= 2) ++ans;
        var isprime = Enumerable.Repeat(true, n + 1).ToArray();
        for (var i = 2; i <= n; ++i)
        {
            if (isprime[i])
            {
                for (var j = i * 2; j <= n; j += i) isprime[j] = false;
            }
        }
        for (var r = 3; r <= n; r += 2) if (isprime[r])
        {
            var p = (long)r * r - 2;
            if (p > n) break;
            var flg = true;
            for (var i = 3L; i * i <= p; i += 2)
            {
                if (p % i == 0)
                {
                    flg = false;
                    break;
                }
            }
            if (flg) ans += 2;
        }
        WriteLine(ans);
    }
}