#include <iostream>
#include <fstream>

using namespace std;

long N, NPrime=1;
char V[2000005];

void Eratosthenes ()
{
    long i, j;
    for (i=2; i<=N; i+=2)
    {
        V[i]=1;
    }
    for (i=3; i<=N; i+=2)
    {
        if (V[i]==0)
        {
            NPrime++;
            for (j=i; j<=N; j+=i)
            {
                V[j]=1;
            }
        }
    }
}

int main ()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin >> N;
    Eratosthenes ();
    fout << NPrime << "\n";
    fin.close ();
    fout.close ();
    return 0;
}