CF93A.Frames

Throughout Igor K.'s life he has had many situations worthy of attention. We remember the story with the virus, the story of his mathematical career and of course, his famous programming achievements. However, one does not always adopt new hobbies, one can quit something as well.

This time Igor K. got disappointed in one of his hobbies: editing and voicing videos. Moreover, he got disappointed in it so much, that he decided to destroy his secret archive for good.

Igor K. use Pindows XR operation system which represents files and folders by small icons. At that, m icons can fit in a horizontal row in any window.

Igor K.'s computer contains n folders in the D: disk's root catalog. The folders are numbered from 1 to n in the order from the left to the right and from top to bottom (see the images). At that the folders with secret videos have numbers from a to b inclusive. Igor K. wants to delete them forever, at that making as few frame selections as possible, and then pressing Shift+Delete exactly once. What is the minimum number of times Igor K. will have to select the folder in order to select folders from a to b and only them? Let us note that if some selected folder is selected repeatedly, then it is deselected. Each selection possesses the shape of some rectangle with sides parallel to the screen's borders.

在伊戈尔·K的一生中，他曾经历过许多值得铭记的时刻。我们记得那个关于病毒的故事、他数学事业的故事，当然还有他著名的编程成就。然而，人并非总是开启新的爱好，有时也会放弃某些爱好。

这一次，伊戈尔·K对他的一项爱好——视频剪辑与配音——感到极度失望。事实上，他失望到了极点，以至于决定永久销毁自己的秘密视频档案。

伊戈尔·K使用的是 Pindows XR 操作系统，该系统以小图标形式表示文件和文件夹。在任意窗口中，每行水平方向最多可容纳 $ m $ 个图标。

伊戈尔·K 的电脑 D: 盘根目录下共包含 $ n $ 个文件夹。这些文件夹按从左到右、从上到下的顺序编号为 $ 1 $ 至 $ n $（参见图片）。其中，存放秘密视频的文件夹编号为从 $ a $ 到 $ b $（含端点）。伊戈尔·K 希望永久删除这些文件夹，且在整个过程中尽可能减少鼠标框选操作次数，最后仅需按一次 Shift+Delete 即可完成删除。那么，为精确选中编号从 $ a $ 到 $ b $ 的所有文件夹（且仅这些文件夹），伊戈尔·K 所需执行的最少框选次数是多少？请注意：若某个已被选中的文件夹被再次框选，则它将被取消选中。每次框选操作所形成的区域均为边与屏幕边界平行的矩形。

The only line contains four integers n, m, a, b (1 ≤ n, m ≤ 109, 1 ≤ a ≤ b ≤ n). They are the number of folders in Igor K.'s computer, the width of a window and the numbers of the first and the last folders that need to be deleted.

唯一的一行包含四个整数 $n$、$m$、$a$、$b$（$1 ≤ n, m ≤ 10^9$，$1 ≤ a ≤ b ≤ n$）。它们分别表示 Igor K. 的电脑中文件夹的总数、窗口的宽度，以及需要删除的文件夹的起始编号和结束编号。

Print a single number: the least possible number of times Igor K. will have to select the folders using frames to select only the folders with numbers from a to b.

输出一个整数：Igor K. 使用矩形框选择编号从 $a$ 到 $b$ 的文件夹（且仅这些文件夹）所需的最少操作次数。

The images below illustrate statement tests.

The first test:

In this test we can select folders 3 and 4 with out first selection, folders 5, 6, 7, 8 with our second selection and folder 9 with our third, last selection.

The second test:

In this test we can first select all folders in the first row (2, 3, 4, 5), then — all other ones.

下方图片展示了语句测试。

第一个测试：

在此测试中，我们可在第一次选择中选中文件夹 3 和 4，在第二次选择中选中文件夹 5、6、7、8，在第三次（即最后一次）选择中选中文件夹 9。

第二个测试：

在此测试中，我们可首先选中第一行的所有文件夹（2、3、4、5），然后选中其余所有文件夹。