Define a period

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How many working days in year 1980?

Here is the detail of the calculation:

Because 1980 is a leap year, it has 366 days.

Let's remove 52 saturdays and 52 sundays. It remains 262 days.

Now, let's remove 13 public holidays that do not fall during a weekend and we obtain 249 working days in 1980.

Here is the list of these 13 public holidays:

1. New Year's Day : Tuesday, 1 January, 1980
2. Coming of Age Day : Monday, 14 January, 1980
3. Foundation Day : Monday, 11 February, 1980
4. Vernal Equinox Day : Thursday, 20 March, 1980
5. Shōwa Day : Tuesday, 29 April, 1980
6. Children's Day : Monday, 5 May, 1980
7. Marine Day : Monday, 21 July, 1980
8. Respect-for-Aged Day : Monday, 15 September, 1980
9. Autumnal Equinox Day : Tuesday, 23 September, 1980
10. Health and Sports Day : Monday, 13 October, 1980
11. Culture Day : Monday, 3 November, 1980
12. Labor Thanksgiving Day (observance) : Monday, 24 November, 1980
13. Emperor's Birthday : Tuesday, 23 December, 1980

And here are the 3 public holidays falling on a weekend:

1. Constitution Memorial Day : Saturday, 3 May, 1980
2. Greenery Day : Sunday, 4 May, 1980
3. Labor Thanksgiving Day : Sunday, 23 November, 1980