CF40C.Berland Square

Last year the world's largest square was built in Berland. It is known that the square can be represented as an infinite plane with an introduced Cartesian system of coordinates. On that square two sets of concentric circles were painted. Let's call the set of concentric circles with radii 1, 2, ..., K and the center in the point (z, 0) a (K, z)-set. Thus, on the square were painted a (N, x)-set and a (M, y)-set. You have to find out how many parts those sets divided the square into.

去年，世界上最大的正方形在贝尔兰建成。已知该正方形可表示为一个引入了笛卡尔坐标系的无限平面。在该正方形上绘制了两组同心圆。我们将以点 $(z, 0)$ 为圆心、半径分别为 $1,\,2,\,\dots,\,K$ 的同心圆集合称为 $(K,\,z)$-集。因此，在该正方形上绘制了一个 $(N,\,x)$-集和一个 $(M,\,y)$-集。你需要求出这些集合将正方形划分成了多少个区域。

The first line contains integers N, x, M, y. (1 ≤ N, M ≤ 100000,  - 100000 ≤ x, y ≤ 100000, x ≠ y).

第一行包含整数 $N$、$x$、$M$、$y$。（$1 \leq N, M \leq 100000$，$-100000 \leq x, y \leq 100000$，$x \neq y$）

Print the sought number of parts.

输出所求的部分数量。

Picture for the third sample:

第三个样例的图片：