1!+2!+3!这种的
import java.util.Scanner;
public class Welcome{
public static void main(String[] args ) {
Scanner input = new Scanner(System.in);
int n,sum=0,result=1;
n = input.nextInt();
for(int i=n;i>=1;i--) {
result *= i;
sum += result;
}
System.out.print(sum);
}
}