//Include
#include <fstream>
using namespace std;

//Constante
const int MAX_SIZE = (int)2e6+1;

//Variabile
ifstream in("ciur.in");
ofstream out("ciur.out");

int n;
int answer = 1;

bool noPrime[MAX_SIZE];

//Main
int main()
{
	in >> n;
	
	for(int i=3 ; i<=n ; i+=2)
	{
		if(!noPrime[i])
		{
			++answer;
			for(int j=i+i; j<=n ; j+=i)
				noPrime[j] = true;
		}
	}
	out << answer;
	
	in.close();
	out.close();
	return 0;
}