import java.util.Scanner;

public class Back_1834 {
    public static void main(String[] args){
        //1.입력
        Scanner sc=new Scanner(System.in);
        // 1-1. 자연수 N 입력
        long N = sc.nextInt();             
        long sum=0;                            //몫 이랑 나머지랑 같을려면 N이하여야함
        long num1=0;
        sc.close();
        for(int i=1;i<N;i++){
            num1=(N+1)*i;
            if((num1/N)>=N){
                break;
            }
            if(N==1){
                System.out.println(1);
            }
            sum+=num1;
        }
        System.out.println(sum);
    }
}