#include <iostream>
#include <fstream>
#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

const int nmax = 2e6+10;

vector<short int> eratostene(nmax,0);
int n;

int main(){
	fin >> n;
	int ans = 0;
	eratostene[1] = eratostene[0] = 1;
	for(int i = 2; i <=n; i++){
		if(!eratostene[i]){
			ans++;
			for(int j = i*2; j <=n; j += i){
				eratostene[j] = 1;
			}
		}
	};
	fout << ans;
	return 0;
}