Berland Square

题意翻译

集合(K,z)是以点(z,0)为圆心，分别以1、2、………K 为半径画出的同心圆。在平面上画了一个(N,x)集和一个(M,y)集，你必须找出这些集合把平面分成了多少部分。 输入格式 第一行包含整数N x M y （1<=N,M<=100000,−100000<=x,y<=100000,x！=y） 输出格式 一个整数

题目描述

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.

输入输出格式

输入格式

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

输出格式

Print the sought number of parts.

输入输出样例

输入样例 #1

1 0 1 1

输出样例 #1

4

输入样例 #2

1 0 1 2

输出样例 #2

3

输入样例 #3

3 3 4 7

输出样例 #3

17

说明

Picture for the third sample: