We say an integer n is naoish if n≥90 and the second-to-last digit of n (in decimal notation) is equal to 9. For example, 10798, 1999 and 90 are naoish, whereas 9900, 2009 and 9 are not. Nino expresses 2020 as a sum:
where each of the nj is naoish.
What is the smallest positive number k for which Nino can do this?