Write down the natural numbers 1, 2, 3, ... in order to form a multi-digit number "123456789101112...". When a certain number N is written, the formed multi-digit number is exactly divisible by 90 for the first time. May I ask: What is N?
将自然数1，2，3，…，依次写下去形成一个多位数"123456789101112…"．当写到某个数N时，所形成的多位数恰好第一次能被90整除．请问：N是多少？
<result>80</result>