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

long long Ciur(long long number){
	int vector[2000005];
	long long nr = 0;
	for (int i = 2; i <= number; i += 1){
		if(vector[i] == 0){
			nr++;
		 for(int j = i + i; j <= number; j += i){
			vector[j] = 1;
		}
	  }
	}
	return nr;
}

int main(){
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
    long long n, rez;
	fin >> n;
	rez = Ciur(n);
	fout << rez;
	return 0;
}