// #include <iostream>

#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");
int v[2000001];
int ciur(int n)
{
	for (int i = 0; i <= n; i++)
		v[i] = 0;
	v[0] = 1;
	v[1] = 1;
	int nr = 0;
	for (int i = 2; i <= n; i++)
		if (!v[i])
		{
			nr++;
			for (int j = 2 * i; j <= n; j += i)
				v[j] = 1;
		}
	return nr;
}
int main()
{
	int n;
	cin >> n;
	cout << ciur(n);
	return 0;
}