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IMO 2007 — Complete Shortlist Question 2

IMO Shortlist · IMO 2007 — Complete Shortlist

Question 2

Consider those functions $f: \mathbb{N} \rightarrow \mathbb{N}$ which satisfy the condition

$$
f(m+n) \geq f(m)+f(f(n))-1
$$

for all $m, n \in \mathbb{N}$. Find all possible values of $f(2007)$.

($\mathbb{N}$ denotes the set of all positive integers.)