Problem Statement

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.

Constraints

• $-10^6 \leq L \leq R \leq 10^6$
• $-10^6 \leq D \leq U \leq 10^6$
• All input values are integers.

Input

The input is given from Standard Input in the following format:

L R D U

Output

Output the answer.