**I. 245.** Six families have just moved into a new house with 6 flats in Twitter Street. Each of them likes to have a little chat with the other families. The guest tells everything of him- or herself to the inviter, all information he or she knows about the others, including their previous address. Of course, the inviter also shares all known information.

Determine at least how many meetings are needed so that each family knows of every other's original address.

Your solution should be prepared by using a spreadsheet application. Each line records a meeting (beginning with line 4). Column `A` contains the number of the inviter family, while column B the guest. Families are numbered from 1 to 6.

The result should appear in cell `A1`. (In the *example* ```23 találkozás szükséges`'' is ```23 meetings are necessary`''.) Cell `A1` should remain empty, if the given appointments are insufficient to realize the desired final state.

You may use auxiliary cells, program modules and macros however can not be used. You can assume that altogether at most 300 meetings will take place.

Your spreadsheet (`i245.xls`, `i245.ods`, ...) together with a short documentation (`i245.txt`, `i245.pdf`, ...) -- also describing the name and version number of the spreadsheet application, further a brief description of your solution--should be submitted in a compressed file (`i245.zip`).

(10 points)

**Deadline expired on 11 October 2010.**