#include <iostream>
#include <cmath>
#include <fstream>

using namespace std;

int main()
{
	int n, i, k=0, c, v[299999];

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

f>>n;
if (n>=2)
k++;
	for (i = 3; i <= n; i+=2)
	{
		v[i] = 0;

		for (c = 2; c <= sqrt(i); c++)
		if (i % c == 0)
			v[i] = 1;

		if (v[i] == 0)
			k++;

	}

	g<<k;



}