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OBM 2025 Problem 1

    Prove que existe um inteiro positivo nn e 2n2n números reais não negativos

    0≤a1≤a2≤a3≤…≤ane0≤b1≤b2≤b3≤…≤bn0 \le a_1 \le a_2 \le a_3 \le \ldots \le a_n \quad \text{e} \quad 0 \le b_1 \le b_2 \le b_3 \le \ldots \le b_n

    satisfazendo as três propriedades a seguir:

    (i) a1+a2+⋯+an≥20252025a_1 + a_2 + \cdots + a_n \ge 2025^{2025};

    (ii) b1+b2+⋯+bn≥20252025b_1 + b_2 + \cdots + b_n \ge 2025^{2025};

    (iii) c1+c2+⋯+cn≤120252025c_1 + c_2 + \cdots + c_n \le \dfrac{1}{2025^{2025}}, onde ci=min⁡{ai,bi}c_i = \min\{a_i, b_i\} para todo i∈{1,2,…,n}i \in \{1, 2, \ldots, n\}.

    Além disso, encontre o menor inteiro positivo nn com tal propriedade.

    Official text Brazilian Mathematical Olympiad 2025 official paper, page 1. Quoted with source.

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