MEMO 2014 ekipno problem 4


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24. rujna 2014.
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In Happy City there are 2014 citizens called A_1, A_2, \ldots, A_{2014}. Each of them is either happy or unhappy at any moment in time. The mood of any citizen A changes (from being unhappy to being happy or vice versa) if and only if some other happy citizen smiles at A. On Monday morning there were N happy citizens in the city.
The following happened on Monday during the day: citizen A_1 smiled at citizen A_2, then A_2 smiled at A_3, etc., and, finally, A_{2013} smiled at A_{2014}. Nobody smiled at anyone else apart from this. Exactly the same repeated on Tuesday, Wednesday and Thursday. There were exactly 2000 happy citizens on Thursday evening.
Determine the largest possible value of N.
Izvor: Srednjoeuropska matematička olimpijada 2014, ekipno natjecanje, problem 4