#include <fstream>
using namespace std;
int main()
{
	int v[2000000],i,n,j,nr=0;
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	fin>>n;
	for (i=2;i<=n;i++) v[i]=1;
	for (i=2;i<=n;i++)
		{
			if (v[i]==1) 
			{   
				nr++;
				for (j=i+i;j<=n;j=j+i) v[j]=0;
			}
		}
	fout<<nr;
	fout.close();
	fin.close();
	return 0;
}