ИМКТ 2023 Нейронные сети

Problem B. Second Best ≡

Given the sequence of integers A₁, A₂, …, A_N, find a number A_s such that there exists exactly one A_m > A_s, and for all k ≠ m A_k ≤ A_s.

Input contains N followed by A₁ A₂… A_N.

Output should contain a single integer — A_s, or  − 1 if no such number exists.

1 ≤ N ≤ 1000000, 0 ≤ A_i ≤ 10⁹,

No.	Input file (`input.txt`)	Output file (`output.txt`)
1	`3 1 2 3`	`2`
2	`4 3 3 2 3`	`-1`