P9779 [HUSTFC 2023] Indeterminate Multiple-Choice Question


There is an indeterminate multiple-choice question with a total of $n$ options. Its correct answer contains at least one option. Since the question and the options are hard to understand, you plan to pass the question by trying every possible answer. Initially, none of the options are selected. You may perform the following operations any number of times: - Select an option that is currently not selected. - Deselect an option that is currently selected. Once your selected set of options matches the correct answer, you will pass the question immediately. Before you start trying, you wonder: in the worst case, at least how many operations are needed to pass the question?

A single line contains an integer $n\ (1\le n \le 20)$, representing the number of options.

Output an integer, representing the minimum number of operations needed to pass the question in the worst case.

The image is unrelated to the problem. Translated by ChatGPT 5