AT_abc449_d [ABC449D] Make Target 2

There is a two-dimensional coordinate plane. A lattice point with coordinates $ (x, y) $ is painted black if $ \max(|x|, |y|) $ is even, and white if it is odd. Among the pairs of integers $ (x, y) $ satisfying $ L \leq x \leq R $ and $ D \leq y \leq U $ , find the number of those for which the point $ (x, y) $ is painted black.

The input is given from Standard Input in the following format: > $ L $ $ R $ $ D $ $ U $

Output the answer.

### Sample Explanation 1  As shown in the figure above, the answer is $ 10 $ . ### Constraints - $ -10^6 \leq L \leq R \leq 10^6 $ - $ -10^6 \leq D \leq U \leq 10^6 $ - All input values are integers.