#include <iostream>
#include <fstream>
#include <cmath>
#include <vector>
#include <queue>
#include <deque>
#include <list>
#include <string>
#include <algorithm>
using namespace std;
ifstream ff("ciur.in");
ofstream gg("ciur.out");

#define max 2000000
int n, r;
unsigned char pp[max/8+13];

void ciu(){
	int i=2, l=(int)sqrt(max);
	while(i<=l){
		while(pp[i>>3]&(1<<(i&7)))i++;
		for(int j=i*i;j<=max;j+=i)pp[j>>3]|=1<<(j&7);
		i++;
	}
}

int main(){
	ff >> n;
	ciu();
	for(int i=2;i<=n;i++)
		if(pp[i>>3]&(1<<(i&7)))continue; else r++;
	gg << r << "\n";
	return 0;
}