#include<iostream>
#include<fstream>
using namespace std;

int main(){

	ifstream f("ciur.in");
	ofstream o("ciur.out");
	int n = 0; f >> n;
	bool a[2000001];
	int nr = 0;

	for (int i = 0; i < n; i++){
		a[i] = false;
	}
	for (int i = 2; i < n ; i++)
	{
		if (a[i]==false){
			nr++;
			for (int j = i; j < n; j += i){
				a[j] = true;
			}
		}
	}

	o << nr;
    o.close();
	return 0;
}