#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n, i, j, nr=0;
    bool prime [ 2000001 ] ;
    f>>n;
    for (j=4; j<=n; j=j+2)
    {
        prime[j]=1;
    }
    for (i=3; i*i<=n; i=i+2)
    {
        if (prime[i]==0)
        {
            for (j=i*i; j<=n; j=j+i)
            {
                prime[j]=1;
            }
        }
    }
    for (i=1; i<=n; i=i+2)
    {
        if (prime[i]==0)
        {
            nr++;
        }
    }
    g<<nr;
    return 0;
}