#include <fstream>
#include <math.h>
using namespace std;
unsigned int a[2000009];
int main()
{
	unsigned int k,m,i,n;
	ifstream f1("ciur.in");
	f1>>n;
	f1.close();
	m=n;
	for (i=1;i<=n;i++) a[i]=i;
	for (i=2;i<=sqrt(n);i++) if (a[i]!=0)  for (k=2*i;k<=n;k=k+i) {a[k]=0;m--;}
	for (m=i=0;i<=n;i++) if (a[i]!=0) m++;
	ofstream f2("ciur.out");
	f2<<m-1;
	f2.close();
	return 0;
}