Compute the sum of consecutive integers starting with $ M $ and ending with $ N $.

Input

The only line of input contains two integers $ M $ and $ N $. ($ -10000 \le M \le N \le 10000 $)

Output

Output $ \displaystyle \sum_{i=M}^{N} i $, i.e. the sum of all integers start from $ M $ and ending with $ N $.

You can learn more about the summation notation $ \displaystyle \left(\sum\right) $ here.