Question
Odd Pairs

Given an integer N, determine the number of pairs (A,B) such that:
       1 <= A,B <= N
        A+B is odd.

Input
The only line of input contains an integer N.

Constraints:
1 ≤ N ≤ 1000000000
Output
Return the number of required pairs.
Example
Sample Input:
1
Sample Output:
0
Explanation
There are no pairs satisfying the given conditions.

Sample Input:
2
Sample Output:
2
Explanation
The pairs satisfying both conditions are: (1,2) and (2,1).

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