#include <algorithm>
#include <bitset>
using namespace std;

#define DIM 2000005

bitset <DIM> viz;
int n,nrt;

void solve ()
{
    int i,j;

    for (i=2; i<=n; ++i)
        if (!viz[i])
        {
            ++nrt;
            for (j=2*i; j<=n; j+=i)
                viz[j]=1;
        }
    printf ("%d",nrt);
}

int main ()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);

    scanf ("%d",&n);
    solve ();

    return 0;
}