Sum of even numbers from 1 to N

Java Easy math

Task «Sum of even numbers from 1 to N»

Write a program that calculates the sum of all even numbers from 1 to a given number N inclusive. If N is less than 2, the sum is considered equal to 0. The number N is a natural number and does not exceed 1000.

Input Format

Integer N (1 ≤ N ≤ 1000).

Output Format

One integer — the sum of even numbers from 1 to N.

Examples

Example 1

INPUT

10

OUTPUT

30

Example 2

INPUT

1

OUTPUT

0

main.java