int long unsigned i,vprim [100000] = {2};
int long unsigned  prim(int long unsigned  a,int long unsigned K)
{
	for(i=0;i<K;i++)
		if(a%vprim[i] == 0)
			return 0;
	vprim[i]=a;
	return 1;
}
 
int main(void)
{
	int long unsigned  i=1,N=13,K=1;
	freopen("ciur.in","r",stdin);
		scanf("%ld",&N);
	fclose(stdin);
	for(i=3;i<=N;i+=2)
	{
		if (prim(i,(int long unsigned) sqrt(K)) K++;
	}
	freopen("ciur.out","w",stdout);
		printf("%ld",(int long unsigned) K);
	fclose(stdout);
	return 0;
}