Add (+) or (-)?
Source: Indonesia National Math Olympiad 2021 Problem 1 (INAMO 2021/1)
November 8, 2021
combinatorics
Problem Statement
On the whiteboard, the numbers are written sequentially: . Andi has to paste a (plus) sign or (minus) sign in between every two successive numbers, and compute the value. Determine the least odd positive integer that Andi can't get from this process.