#include <fstream>
using namespace std;

fstream f ("ciur.in");
ofstream g ("ciur.out");
char a[2000001];
int n,i,j,nr;
int main()
{
	f>>n;
for (i=2;i<=n;i++)
{	if (a[i]==0)
	{nr++;
	for (j=2;j<=n/i;j++)
		a[i*j]=1; 
	}
}
g<<nr;
g.close();
return 0;
}