#include<iostream.h>
#include<fstream.h>
#include<math.h>
long int n;
long i,j,k;
int a[2000001];
int main()
{
	fstream f("ciur.in",ios::in);
	fstream g("ciur.out",ios::out);
	f>>n;
	a[2]=1;
	for(i=3;i<=n;i=i+2)
		a[i]=1;
	for(i=3;i<=n;i=i+2)
		if(a[i]==1) {
					   
					   j=2*i;
					   while(j<=n) {
						   a[j]=0;
						   j=j+i;
						}
					}
		k=0;
	for(i=2;i<=n;i=i+2)
	if(a[i]==1)k++;
	g<<k;
	f.close();g.close();
	return 0;
}