Even Odds · Interview Problem

Codeforces

Easy

Math

Arrays

Even Odds

Find the $k$ -th number in a sequence formed by listing all odd numbers up to $n$ first, then all even numbers up to $n$ .

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Codeforces 318A

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Problem Statement

Problem

You are given two integers $n$ and $k$ . Consider the sequence of numbers from $1 $to$ n$ arranged in this order:

All odd numbers in increasing order
All even numbers in increasing order

Your task is to output the $k$ -th number in this sequence.

For example, when $n=10$ , the sequence is:

1 3 5 7 9 2 4 6 8 10

and the 7-th element is 4.

Goal

Return the value at position $k$ without constructing the entire sequence if possible.

Input Format

A single line contains two integers $n$ and $k$ .
$1 \le k \le n$ .

Output Format

Print one integer: the $k$ -th element of the described ordering.

Constraints

$1 \le k \le n$
$1 \le n \le 10^9$

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