Fir Trees#4193
Just before the New Year, an alley in the city park had fir trees planted in a row, with equal distances between each neighboring tree. After the New Year holidays, only fir trees remained, still maintaining the equal distances between them.
Since there is no way to catch the thieves, we need to determine how many different ways the trees could have been cut down.
You will be given two natural numbers, and (1 \leq M, N \leq 1000).
Output the number of possible ways to cut down the trees.
Example 1