Score : $100$ points
We have $N+M$ balls, each of which has an integer written on it.
It is known that:
Find the number of ways to choose two of the $N+M$ balls (disregarding order) so that the sum of the numbers written on them is even.
It can be shown that this count does not depend on the actual values written on the balls.
Input is given from Standard Input in the following format:
Print the answer.
For example, let us assume that the numbers written on the three balls are $1,2,4$.
Thus, the answer is $1$.