How would I do it the vacations are a little different, i.e.

after 1 year of work they receive 5 days vacations
for the 2nd, 3rd, and 4th year, vacation days equal 10 days
for the 5th, 6th, 7th, 8th, 9th year vacation days equal 15 days.
and then 10 years on, total vacation days equal 20.

1yr=5 days
2, 3, 4 yr= 10 days
5,6,7,8,9 yr = 15 days
10 and on = 20 days

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thanks,
John