Question

Edward and Maths Competition

3

2

6

9

11

30

Edward participated in one maths competition. He was asked to find the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and N (inclusive). The order does not matter.

Input

The input line contains only one input N.

2≤N≤100

N is an integer.

**Constraints**2≤N≤100

N is an integer.

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 N (inclusive).

Example

**Sample Input 1**

3

**Sample Output 1**

2

**Sample Input 2**

6

**Sample Output 2**

9

**Sample Input 3**

11

**Sample Output 3**

30