#include<iostream>
#include<fstream>
using namespace std;
int main(void)
{
	long i,j,n,terminat=0,a[100000],b[100000],e,nrdiv=1,putere,maxd,min,contor=0;
	fstream g,f;
	f.open("ciur.in",ciur::in)
	g.open("ciur.out",ios::out);
	f>>n;
	for (i=0;i<(n-1)/2;i++)
		a[i]=2*i+3;
	
	b[0]=2;j=0;
	while (!terminat)
	{
		for (i=0;i<(n-1)/2;i++)
			if (a[i]%b[j]==0)
				a[i]=0;
		for (i=0;a[i]==0;i++);
		if (i<(n-1)/2)
			{j++; b[j]=a[i];}
		else
		terminat=1;
	}
	g<<j;
}