Score : 100 points
How many ways are there to choose two distinct positive integers totaling N, disregarding the order?
Input is given from Standard Input in the following format:
N
Print the answer.
4
1
There is only one way to choose two distinct integers totaling 4: to choose 1 and 3. (Choosing 3 and 1 is not considered different from this.)
999999
499999