#include <fstream>
#include <vector>
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

vector<bool> x(2000002,0);
long n,i,s,j;

int main()
{
in>>n;
s=n-1;
for(i=2; i<=n/2; i++)
	if(!x[i])
		{
		for(j=i*2; j<=n; j+=i)
			if(!x[j])
				{
				x[j]=1;
				s--;
				}
		}
out<<s;
}