#include<fstream>
#define dmax 2000002
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
	int n;
	
	in>>n;
	in.close();
	
	bool x[dmax];
	
	int nr = 0;
	
	for(int i=2; i <= n; i++)
		x[i] = 1;

	for(int i=2; i <= n; i++)
		if(x[i] == 1)
		{
			nr++;

			for(int j=i; j <= n; j+=i)
				x[j] = 0;
		}

	out<<nr;
	
	out.close();
	return 0;
}