import java.util.Scanner;
public class Main{
    public static void main(String[] agrs){
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int res=0;
        for(int i=1;i<n;i++){
            if(i*i%n*2<n)
            res++;
        }
        System.out.println(res);
    }
}