#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
const int Nmax=2000001;
int n,nr,i,j;
char a[Nmax];
int main()
{	f>>n;
	for(i=2;i<=n;i++)
		if(!a[i]) 
		{	nr++;
			for(j=i+i;j<=n;j+=i) a[j]=1;
		}
	g<<nr<<"\n";
	g.close();
	return 0;
}