Sum of Even Numbers up to N
Add up the even numbers from 1 to N.
Input format
One line with an integer N (at least 1).
Output format
Print the sum of every even number from 1 to N inclusive.
Constraints
- Values fit in a 64-bit signed integer
- Trailing whitespace and a trailing newline are ignored by the judge
Read from stdin, write to stdout. Sample cases below show the exact format.
Sample cases
Example 1
Input
10Expected output
30Example 2
Input
7Expected output
12