#include <iostream>
#include <fstream>
#include <math.h>
#define sqr(x) x*x


using namespace std;

ifstream input("ciur.in");
ofstream output("ciur.out");



int main()
{
    int n,i,j,nr_prime_pana_la_n=0;
    input>>n;
    bool numere[2000001];

    for (i=2; i<=n; i++)
    {
        numere[i]=true;
    }
    cout<<numere[2];

    for (i=2; i<=n; i++)
        if(numere[i])
                {
                    nr_prime_pana_la_n+=1;
                    for (j=i+i; j<=n; j+=i)
                        numere[j]=false;
                }



    output<<nr_prime_pana_la_n;
    return 0;
}