#include <bits/stdc++.h>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

void SieveOfEratosthenes(int n)
{int c=0;
    bool prime[n+1];
    memset(prime, true, sizeof(prime));

    for (int p=2; p*p<=n; p++)
    {

        if (prime[p] == true)
        {

            for (int i=p*2; i<=n; i += p)
                prime[i] = false;
        }
    }


    for (int p=2; p<=n; p++)
       if (prime[p])
          c++;
    g<<c;
}


int main()
{
    int n;
    f>>n;
    SieveOfEratosthenes(n);
    return 0;
}