Description

Calculate the sum of all odd numbers less than the input integer. For example, if the input is 8, the output should be the sum of 1 + 3 + 5 + 7; if the input is 7, the output should be the sum of 1 + 3 + 5.

Input Format

A single line containing a positive integer N.

Output Format

Output the sum of all odd numbers less than the positive integer N.

8

16

7

9

源码

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