#include <iostream>
#include <fstream>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int n,prime[2000001],nr = 0;

int main ()
{
    fin >> n;
    for (int i = 2; i <= n; i++)
    {
        prime[i] = 1;
    }
    for (int i = 2; i <= n; i++)
    {
        if (prime[i] > 0)
        {
            nr++;
            for (int j = i + i; j <= n; j += i)
            {
                prime[j] = 0;
            }
        }
    }
    fout << nr;
    return 0;
}