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

using namespace std;

int main()
{
	int n, i, k=0, v[100], j, c;

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

	f>>n;
	if (n >= 2)
		k++;	//cout << 2 << " ";

	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++; //cout<<i<<" ";

	}

	g<<k;
	//cout << k;


}