IMO Shortlist 1999 problem C3


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A biologist watches a chameleon. The chameleon catches flies and rests after each catch. The biologist notices that:

- the first fly is caught after a resting period of one minute;
- the resting period before catching the 2m^{th} fly is the same as the resting period before catching the m^{th} fly and one minute shorter than the resting period before catching the (2m+1)^{th} fly;
- when the chameleon stops resting, he
catches a fly instantly.


- How many flies were caught by the chameleon before his first resting period of 9 minutes in a row ?
- After how many minutes will the chameleon catch his 98^{th} fly ?
- How many flies were caught by the chameleon after 1999 minutes have passed ?
Izvor: Međunarodna matematička olimpijada, shortlist 1999