请问这是哪里错了 答案也不正确

你没读懂题目啊

int n; 
long long an = 0;
scanf( "%d", &n );
if  (n == 1 || n == 2)
{  
  printf("0");
  return;
}
for ( int i = 3; i<=n ; i++ )
{
  an = an + (i-2)*(i-1)*n;
}
//最后输出 an