#include<fstream>
using namespace std;
int main ()
{
	long int x[20001],n,i,j,k=0;
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	in>>n;
	for(i=1;i<=n;i++)
		x[i]=0;
	for(i=2;i<=n;i++)
		{if (x[i]==0) for(j=2*i;j<=n;j=j+i)
			           x[j]=1;
		
		}
	for(i=2;i<=n;i++)
		if(x[i]==0) k++;
	out<<k;
	in.close();
	out.close();
	
return 0;
}