#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, c;
bool a[2000005];

int prime(int n){
	for(int i = 2; i <= n; ++i){
		if(a[i]==true){
			for(int j = i*i; j <= n; j+=i){
				a[j]=false;
			}	
		c++;
		}	
	}
	return c;
}

int main(){
	fin >> n;
	for(int i = 2; i <= n; ++i){
		a[i] = true;
	}
	fout << prime(n);

}