Find the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive). The order does not matter.

-----Constraints-----
- $2\leq K\leq 100$
- K is an integer.

-----Input-----
Input is given from Standard Input in the following format:
K

-----Output-----
Print the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive).

-----Sample Input-----
3

-----Sample Output-----
2

Two pairs can be chosen: (2,1) and (2,3).

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