#include <fstream>

using namespace std;

#define infile "ciur.in"
#define outfile "ciur.out"

int main (void)
{
	ifstream in(infile);
	int n,j,phi[2000005],i,count=0;
	in>>n;
	for (i=1;i<=n;i++) 
		phi[i]=i;
	for (i=2;i<=n;i++)
		if (phi[i]==i)
		{
			count++;
			for (j=i+i;j<=n;j+=i) 
				phi[j]=0;
		}
	ofstream out(outfile);
	out<<count;
	in.close();
	out.close();
	return 0;
}