#include<fstream>
using namespace std;

bool Ciur[2000003];

int Calculeaza(int N)
{
	int count=0;
	for (int nr=2; nr<=N; nr++)
	{
		if (!Ciur[nr]){
			count++;
			for (int i=nr*2; i<=N; i+=nr)
				Ciur[i] = true;
		}
	}
	
	return count;
}

int main()
{
	ifstream in ("ciur.in");
	ofstream out ("ciur.out");
	
	int n; in>>n;
	out<<Calculeaza(n)<<"\n";
	
	in.close();
	out.close();
	return 0;
}