#include <iostream>
	
#include <fstream>
	
using namespace std;
	
 
	
long long Ciur(long long number){
	
	bool vector[2000001];
	
	long long nr = 0;
	
	for (int i = 2; i <= number; i = i + 1){
	
		vector[i] = 1;}
		for (int i = 2; i <= number; i = i + 1){
	
		      if(vector[i]){
		      	nr++;
		      

	
		for(int j = i + i; j <= number; j = j + i){
	
			vector[j] = 0;
	
		}
	}
		
	
	}
	
	
	return nr;
	
}
	
 
	
int main(){
	
	ifstream fin("ciur.in");
	
	ofstream fout("ciur.out");
	
    long long n;
	
	fin >> n;

	fout << Ciur(n) << '\n';
	
	return 0;
	
}