#include <fstream>
#include <iostream>
using namespace std;

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

const unsigned int MAXN = 2000001;
char neprim[MAXN];

int main ()
{
	unsigned int N;
	in >> N;
	in.close();
	
	unsigned int i,j,nrprime=1;
	for (i=3; i<=N; i+=2) {
		if (!neprim[i]) {
			++nrprime;
			for (j=i*i; j<=N; j+=i) neprim[j]=1;
		}
	}
	out<<nrprime<<'\n';
	out.close();
	return 0;
}