import java.util.Scanner;

public class G {
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        while (cin.hasNext()) {
            long p = 1;
            int n = cin.nextInt();
            for (int t = n; t >= 1; t -= 2) p *= t;
            System.out.println(p);
        }
        cin.close();
    }
}