Let \( \mathbb{Z}^+ \) be the set of positive integers. Suppose that \( f : \mathbb{Z}^+ \to \mathbb{Z}^+ \) satisfies the following conditions.
i) \( f(f(x)) = 5x \).
ii) If \( m \geq n \), then \( f(m) \geq f(n) \).
iii) \( f(1) \neq 2 \).
Find \( f(256) \).
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2013-02 Functional equation,
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