And we have an right answer! Thanks to both Eddie and John for their right answer. Very well done!
You are at a party with a friend and 30 people are present including you and the friend. Your friend wants to make a wager with you if there are two people that share their birthday date, he will give you 100$, however, you shall give him 100$ if nobody shares their birth date. Would you accept the wager ? Explain why.