#include	<iostream>
#include	<fstream>

using namespace std;

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

int prime[2000005], numbers;

int main()
{
	int N;
	fin >> N;

	for(int i = 2; i <= N; i++)
		prime[i] = 1;

	for(int i = 2; i <= N; i++)
	{
		if(prime[i])
		{
			numbers += 1;
			for(int j = i + i; j <= N; j += i)
				prime[j] = 0;
		}
	}

	fout << numbers;
	return 0;
}