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
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).
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).