import java.util.Scanner;

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