G. Gusteseu and Maynotauro
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

The ancient and bustling city of Cnossos was renowned for its mysterious labyrinth, composed of a set of $$$N \times M$$$ square rooms arranged in an $$$N$$$ by $$$M$$$ grid. The rooms were named by an ordered pair $$$(A,B)$$$, where $$$A$$$ represented the row and $$$B$$$ represented the column in which the room was located. The entrance to the labyrinth was at position $$$(1,1)$$$.

In this city, there was a fearless adventurer named Gusteseu. He was known for his courage and skill in unraveling the most complex riddles.

One day, Gusteseu received an extraordinary mission: to explore the labyrinth and find a legendary treasure rumored to be hidden in its depths. However, there was a daunting challenge in Gusteseu's path. The labyrinth was inhabited by a creature feared by all: the mighty Maynotauro.

The Maynotauro, a creature with the body of a woman and the head of a bull, guarded the labyrinth's entrance and protected the path to the treasure. Its dwelling was known as the Maynotauro's room, located at position $$$(X,Y)$$$ in the labyrinth.

Determined to complete his mission, Gusteseu knew he had to avoid the Maynotauro's room. He understood that passing through that room would result in his capture and failure in the quest for the treasure.

Due to the unpleasant conditions within the labyrinth, Gusteseu aimed to reach the treasure room as efficiently as possible, passing through the fewest number of rooms. He disregarded any other ways of achieving this path.

With his sharp mind and expertise in competitive programming, Gusteseu decided to employ his skills to calculate the number of efficient ways to reach the treasure room, located at position $$$(N,M)$$$, without passing through the Maynotauro's room.

Input

The input consists of a single line with four integers separated by spaces: $$$N$$$, $$$M$$$ ($$$1 \leq N, M \leq 30$$$), $$$X$$$ ($$$1 \leq X \leq N$$$), and $$$Y$$$ ($$$1 \leq Y \leq M$$$).

$$$N$$$ and $$$M$$$ indicate the size of the labyrinth and the position $$$(N,M)$$$ of the treasure room.

$$$X$$$ and $$$Y$$$ indicate the position $$$(X,Y)$$$ of the Maynotauro's room.

Output

Print a single number indicating the number of distinct efficient ways to reach the treasure room as calculated by Gusteseu.

Examples
Input
2 3 2 2
Output
1
Input
4 4 3 2
Output
11
Input
30 30 15 15
Output
23844478996709040
Note

Example of test case 1:

There is only one valid way, which is highlighted.