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BALKAN-SL 2009 C2

    Let A1,A2,…,AmA_1, A_2, \ldots , A_m be subsets of the set {1,2,…,n}\{ 1,2, \ldots , n \} , such that the cardinal of each subset AiA_i , such 1≤i≤m1 \le i \le m is not divisible by 3030 , while the cardinal of each of the subsets Ai∩AjA_i \cap A_j for 1≤i,j≤m1 \le i,j \le m , i≠ji \neq j is divisible by 3030 . Prove \begin{align*} 2m - \left \lfloor \frac{m}{30} \right \rfloor \le 3n \end{align*}

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