27. The forty thieves have accumulated a great many treasures, all hidden in a secret cave. They were afraid of forgetting the password to open the door, so they carved a password hint on the door of the cave:
“There is a sequence of fractions: $\frac{1}{1}, \frac{1}{2}, \frac{2}{2}, \frac{1}{2}, \frac{1}{3}, \frac{2}{3}, \frac{3}{3}, \frac{2}{3}, \frac{1}{3}, \frac{1}{4}, \frac{2}{4}, \frac{3}{4}, \frac{4}{4}, \frac{3}{4}, \frac{2}{4}, \frac{1}{4}, \cdots \cdots$. Then $\frac{2020}{2020}$ is the nth number in this sequence?"
So the password to open the door is $\qquad$
$4078381$