Define a period

...

How many working days in year 1977?

Here is the detail of the calculation:

Because 1977 is not a leap year, it has 365 days.

Let's remove 53 saturdays and 52 sundays. It remains 260 days.

Now, let's remove 14 public holidays that do not fall during a weekend and we obtain 246 working days in 1977.

Here is the list of these 14 public holidays:

1. New Year's Day (observance) : Monday, 3 January, 1977
2. Coming of Age Day : Monday, 10 January, 1977
3. Foundation Day : Friday, 11 February, 1977
4. Shōwa Day : Friday, 29 April, 1977
5. Constitution Memorial Day : Tuesday, 3 May, 1977
6. Greenery Day : Wednesday, 4 May, 1977
7. Children's Day : Thursday, 5 May, 1977
8. Marine Day : Monday, 18 July, 1977
9. Respect-for-Aged Day : Monday, 19 September, 1977
10. Autumnal Equinox Day : Friday, 23 September, 1977
11. Health and Sports Day : Monday, 10 October, 1977
12. Culture Day : Thursday, 3 November, 1977
13. Labor Thanksgiving Day : Wednesday, 23 November, 1977
14. Emperor's Birthday : Friday, 23 December, 1977

And here are the 2 public holidays falling on a weekend:

1. New Year's Day : Saturday, 1 January, 1977
2. Vernal Equinox Day : Sunday, 20 March, 1977