Calculate the sum of first n even numbers recursively.

Difficulty: Medium

Phase: 3 · Recursion

XP Reward: 20 XP

Topics: Recursion, Medium

Supported Languages: Python, JavaScript, C, C++, Java

Problem Description

Given N, calculate the sum of the first N even positive numbers (2 + 4 + ... + 2N) recursively. Input Format: Read input from standard input (stdin). Output Format: Print the result to standard output (stdout).

Constraints

-10^9 <= N <= 10^9

Examples

Example 1

Input: 4

Output: 20

Explanation: Sample execution for input 4