#include <iostream>
#include <fstream>

bool nemPrim[2000001] = {};

int main(){
	int primekSzama = 0;
	int n;
	std::ifstream bem("ciur.in");
	bem >> n;
	bem.close();
	nemPrim[0] = true;
	nemPrim[1] = true;
	for(int i = 2; i * i < n; i++){
		if(!nemPrim[i]){
			for(int j = i*i; j <= n; j += i){
				nemPrim[j] = true;
			}
		}
	}
	for(int i = 0; i < n; i++){
		if(!nemPrim[i]){
			primekSzama++;
		}
	}
	std::ofstream kim("ciur.out");
	kim << primekSzama;

	return 0;
}