#include<iostream>
#include<fstream>
using namespace std;
ifstream in ("erostene.in");
ofstream out("erostene.out");
int main ()
{    int n,i,j,a[100000],k;
     in>>n;

for (i=3;i*i<=n;i=i+2)
	if (a[i]==0) 
		for (j=i*i;j<=n;j=j+2*i)
			a[j] =1;

k = 1;

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