# include <stdio.h>
# include <math.h>
int i,n,k,j,a[30000000];
int main ()
{
freopen ("ciur.in","r",stdin);
freopen ("ciur.out","w",stdout);
scanf ("%i",&n);
for (i=2;i<=n;i++)
if (a[i]==0)
{
k++;
for (j=i;j<=n;j=j+i)
a[j]=1;
}

printf ("%i",k);
return 0;
}