#include<fstream>
#include<malloc.h>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

#define NMAX 20000000

int n = 0,nr = 0;
short a[NMAX];

void eratosthenes()
{
	for(int i = 4; i <= n; i+=2)
		a[i] = 1;
	
	nr = 1;
	for(int i = 3; i <= n; i += 2)
	{
		if(!a[i])
		{
			nr++;
			if(i * i <= n)
				for(unsigned long long  j = i * i; j <= n; j += i)
					a[j] = 1;
		}
	}
}

int main()
{
	f>>n;
	
	eratosthenes();
	
	g<<nr;
	
	g.close();
	
	return 0;
}