#include<iostream>
#include<fstream>

using namespace std;

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

int main(void)
{
	int n, prim[2000005] = { 0 }, cnt = 0, i, j;
	fin >> n;
	for (i = 2; i <= n; i++)
		prim[i] = 1;

	for (i = 2; i <= n; i++)
	if (prim[i])
	{
		++cnt;
		for (j = i*i; j <= n; j += i)
			prim[j] = 0;
	}
	fout << cnt << endl;

	return 0;
}