#include <fstream>
#include <string>
using namespace std;


int main()
{
	bool ok[2000000];

	int i, j, n;
	int p = 0;


	ifstream fin("ciur.in");
	j = 2;
	fin >> n;

	for (i = 0; i < n; i++)
		ok[i] = true;

	for (i = 2; i * i <= n; i++)
		if (ok[i])
		{
			j = 2;
			while (i * j <= n)
			{
				ok[i * j] = false;
				j++;
			}
		}
	fin.close();
	ofstream fout("ciur.out");
	for (i = 2; i <= n; i++)
		if(ok[i])
		p++;
	fout << p;
	
	fout.close();
	return 0;
}