#include<iostream>
#include<fstream>
using namespace std;
int prim[2000000];
int N;
int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>N;
	int i, j;
	int numar = 0;
	prim[1] = 0;
	for(i=2 ; i <= N ; i++)
	prim[i] = 1;
	for(i=2 ; i <= N ; i++)
	if(prim[i] == 1)
	{numar++;
	for(j=i+i ; j <= N ; j = j+i)
	prim[j] = 0;
	}
	g<<numar;
}