#include<iostream>
#include<fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out("ciur.out");
bool a[2000004];
int main ()
{    int n,i,j,k;
     in>>n;k=1;

for (i=3;i<=n;i=i+2)
{	if (!a[i]) 
     {  k++;
  		for (j=i*i;j<=n;j=j+2*i)
			a[j]=1;
     }    
}
		
		out<<k;
return 0;
}