#include <iostream>
#include <fstream>

int a[2000001];
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");


int main()
{
	int n, num=0;
	cin >> n;
	for (int i = 2; i <= n; ++i)

	{

		if (a[i] == 0)

		{

			num++;

			for (int j = i * i; j <= n; j += i)

			{

				a[j] = 1;

			}

		}

	}
	cout << num << "\n";
	return 0;
}