#include	<iostream>
#include	<fstream>

using namespace std;

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

int numbers;
bool isPrime[2000005];

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

	for(int i = 2; i <= N; i++)
		isPrime[i] = true;

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