**I. 380.** By using a spreadsheet application it is easy to determine the day of the week for a given date. However, many of these applications cannot interpret dates before 1900 January 1. To handle this situation we can use perpetual calendars that were developed in the pre-computer era. Our perpetual calendar has 3 auxiliary tables. The first auxiliary table (``Évek indexszámai'' in the example) assigns an integer (called index) to each year. The second table (``Hónapok kulcsszámai'' in the example) yields another number (called key) based on the index and the number of the month. Finally, by using the third table (``A kapott számértékhez rendelt nap'' in the example) we find the day of the week from the sum of the key and the number of the day of the month (in the examples, ``Héfő'' is Monday, and ``Szombat'' is Saturday). Let us consider 1848 March 15, for example. The index corresponding to 1848 is 45. The key corresponding to 45 and March is 2. Finally, looking up the sum \(\displaystyle 2+15\) in the third table we get Wednesday.

In this task you should create a spreadsheet to find the day of the week for a given date. The auxiliary tables are available to you in the (UTF-encoded and tabulator-separated) file `tablak.txt`.

1. Read the data file `tablak.txt` to a sheet beginning with cell `A1`, then save this sheet as `oroknaptar` in the default application file format.

2. Now you determine the index corresponding to the given year in two steps. First display-in the cells of row `36` and by using a formula-the row number in which the year (=``Év'') given in cell `C1` appears for each of the columns of the auxiliary table `B5:T35`. If the year does not appear in a particular column, the corresponding cell in row `36` should contain a 0.

3. As a next step, display-in cell `C2` and by using a function-the index of the year in cell `C1`. The index is found in column `A5:A35`; its row number is specified by the non-zero element of row `36`.

4. Next determine the key (=``Kulcs'') and display it in cell `E2`. The key depends on the index computed above and on the number of the month (=``Hónap'') given in cell `E1`. The key should be determined by using the table `A39:M53` and applying a function: columns of this auxiliary table correspond to the months (`B39:M39`), while rows correspond to the indices (`A40:A53`).

5. To determine the day (=``Nap''), display-in cell `G2` and by using a formula-the sum of the key (`E2`) and the number of the day (`G1`).

6. In the last step, determine the name of the day. Locate the sum computed in `G2` by using a formula in the auxiliary table `A57:G63`: the name of the day-to be displayed in cell `I2`-is found in the last column of this table in the row in which the sum appears.

7. Each of the 3 auxiliary tables (`A5:T35`, `A39:M53`, `A57:G63`) should be bordered by thin lines inside and thick lines outside. The content of the 3 cells specifying the date, and that of the cell containing the name of the day should appear in bold with light gray background.

8. By using conditional formatting with bold fonts and dark red color, you should highlight

\(\displaystyle a)\) the year in the range `B5:T35` that appears in cell `C1`,

\(\displaystyle b)\) the month in the column header `B39:M39` that appears in cell `E1`,

\(\displaystyle c)\) the index in the row header `A40:A53` that appears in cell `C2`, and

\(\displaystyle d)\) the integer in the range `B40:M53` that appears in cell `G2 `(as ``Számérték'').