#include<iostream.h>
#include<fstream.h>
int main()
{
	unsigned long long n,i=1,a[200000];
	ifstream f;
	f.open("ciur.in");
	cout<<"n=";
	cin>>n;
	//f>>n;
	for(i=2;i<=n;i++)
		a[i-1]=i;
	int k=0;
	i=1;
	while(i<=n-1)
	{
		if(a[i]!=1) 
		{ 	
			k++;
			for(int j=2;j<=n/2;j++)
			if((j*a[i])!=1) a[j]=1; 
		}
		i++;

	}
	ofstream g;
	g.open("ciur.out");
	cout<<k;
	//g<<k;
	f.close();
	g.close();
	return 0;
	}