import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a= scanner.nextInt();
        long b=1,c=a,d=a;
        long sum=0;
        if (a==0){
            System.out.println(0);
        }else {
            for (int j=0;j<d;j++){
                for (int i=0;i<c;i++) {
                    b = b * a;
                    a--;
                }
                sum=sum+b;
                c--;
                a=c;
                b=1;
            }
            BigInteger e=BigInteger.valueOf(sum);
            System.out.println(e);
        }

    }
}