#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

const int LMAX = 2000005;

bool c[LMAX];

int ciur(int n)
{
	int ans = 0;
	c[0] = c[1] = 1;
	for (int i = 2; i <= n; ++i)
		if (c[i] == 0)
		{
			ans++;
			for (int j = i * i; j <= n; j = j + i)
				c[j] = 1;
		}
	return ans;
}

int main()
{
	int n;
	cin >> n;
	cout << ciur(n);
	return 0;
}