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

int main(){

	ifstream f("ciur.in");
	ofstream o("ciur.out");
	double n = 0; f >> n;
	bool a[20000];
	for (int i = 2; i <= n; i++){
		a[i] = true;
	}
	for (int i = 2; i <= sqrt(n); i++)
	{
		if (a[i]){
			for (int j = i; j <= n / i; j++){
				a[i*j] = false;
			}
		}
	}
	int nr = 0;
	for (int i = 2; i <= n; i++){
		if (a[i]){
			nr++;
		}
	}
	o << nr;

	return 0;
}