import java.util.Scanner;


public class Main_yukicoder242 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        double e = (double)12 * n * (n - 1) * (n - 2) * (n - 3) * (n - 4) / 99 / 98 / 97 / 96 / 95;

        System.out.printf("%.7f\n", e);

        sc.close();
    }
}