/*
ciurul lui eratosthenes infoarena

*/
#include<vector>
#include<string>
#include<string.h>
#include<algorithm>
#include<cstdio>
#include<fstream>
#include<iostream>
#include<ctime>
#include<set>
#include<map>
#include<cmath>

using namespace std;

#define LL long long
#define PII pair<int ,int>
#define PCI pair<char ,int>
#define VB vector <bool>
#define VI vector <int>
#define VC vector <char>
#define WI vector<VI>
#define WC vector<VC>
#define RS resize
#define X first
#define Y second

#define FORN(i,n) for(int i=0;i<n;++i)
#define FOR(i,a,b) for(int i=a;i<=b;++i)
#define FORD(i,a,b) for(int i=a;i>=b;--i)
#define REPEAT do
#define UNTIL(x) while((x))

#define IN_FILE "ciur.in"
#define OUT_FILE "ciur.out"
ifstream f(IN_FILE);
ofstream g(OUT_FILE);

//variables
int n,prime;
VB a;
//other functions
void reading()
{
	f >> n;
	a.RS(n + 1,true);
	f.close();
}
void solving()
{
	FOR(i, 2, n)
	{
		if (a[i])
		{
			++prime;
			for (int j = i + i; j <= n; j += i)
			{
				a[j] = false;
			}
		}
	}
}
void write_data()
{
	g << prime;
}
int main()
{
	reading();
	solving();
	write_data();
}