#include <iostream.h>
#include <fstream.h>
#include <stdio.h>

int n,j,i,contor;
char v[500000000];
int main()
{
ifstream fin("ciur.in");	
ofstream fout("ciur.out");
fin>>n;
for(i=2;i<=n;i++)
	v[i]=1;
for(i=2;i<=n;i++)
	if(v[i])
	{
	contor++;
	for(j=i+i;j<=n;j+=i)
		v[j]=0;
	}
fout<<contor<<'\n';
fin.close ();
fout.close ();
return 0;
}