#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int i,j,nr,n;
bool *prim;
int main()
{
fin>>n;
prim=new bool[n+1];
for ( i = 1; i <= n; i++ )
prim[i]=false;
nr=0;
for (i=2; i<=n; i++)
	{
	if (prim[i]==false) 
	{
	j=2;
	while(i*j<=n) 
	{
	prim[i*j]=true;
	j++;
	}
	nr++;
	}
	}
	fout << nr;
	return 0;
}