#include<iostream>
#include<fstream>
#include<bitset>
using namespace std;
bool v[2000000];
int k,n,i,z;
int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>n;
	z=2;
	while(z<n/2)
	{
	for(i=z;i<=n-1;i=i+z)
	{
		if(v[i]==false)
		{
		if(i%z==0 && i!=z)
			v[i]=true;
		}
		
		
	}
	z=z+1;
	while(v[z]==1 && z<n/2)
		z++;
	}
	for(i=2;i<n-1;i++)
	{
		if(v[i]==false)
			{k=k+1;}
	}
	g<<k;
	return 0;
}