#D4742. Pair
Pair
Pair
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).
Examples
Input
3
Output
2
Input
6
Output
9
Input
11
Output
30
Input
50
Output
625
inputFormat
Input
Input is given from Standard Input in the following format:
K
outputFormat
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).
Examples
Input
3
Output
2
Input
6
Output
9
Input
11
Output
30
Input
50
Output
625
样例
69