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

using namespace std;

int main()
{
	int n, i, k=0, s, v[499999],j;

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

	f >> n;
k++;

	for (i = 3; i <= n; i += 2)
		v[i] = 0;

	for (i = 3; i <= n; i += 2)
	{
		for (j = 3; j <= sqrt(n); j++)
		{
			s = i*j;
			if (s <= n)
			v[s] = 1;
		}
		if (v[i] == 0)
			k++;


	}
g<<k;


}