#include <iostream>
using namespace std;
class Vector2 
{
public:
	int x;
	int y;
public:
	Vector2()
	{
		x = 0;
		y = 0;
	}
	Vector2(int x,int y)
	{
		this->x = x;
		this->y = y;
	}
	
	bool operator ==(Vector2* des)
	{
		return des->x == this->x && des->y == this->y ? true : false;
	}
	~Vector2()
	{
		
	}
};
Vector2** getPosition(Vector2* ma);
int getPath(Vector2 current, Vector2** pos, Vector2* dir);
int main()
{
	Vector2* b = new Vector2();	
	Vector2* ma = new Vector2();
	cin >> b->x >> b->y >> ma->x >> ma->y;
	Vector2* bin = new Vector2(0, 0);
	Vector2** pos = getPosition(ma);
	//cout << ( * pos)[0].x;
	Vector2 a;
	a.x = 0;
	a.y = 0;
	int count = 0;
	long long int path[21][21] = { 0 };
	for (int i = 0; i <= b->x; i++)
	{
		for (int j = 0; j <= b->y; j++)
		{			
			Vector2 current;
			current.x = i;
			current.y = j;
			for (int k = 0; k < 9; k++)
			{
				Vector2* p = new Vector2((*pos)[k].x, (*pos)[k].y);
				if (current == p)//在阻碍点
				{
					current.x = -1;
					break;
				}
				
			}
			if (current.x != -1)
			{
				if (i == 0 || j == 0)
				{
					path[i][j] = 1;
				}
				else
				{
					path[i][j] = path[i - 1][j] + path[i][j - 1];
				}
			}
		}
	}
	cout << path[b->x][b->y];
	//cout << getPath(a, pos, b);
	return 0;
}
Vector2(* pos) = new (Vector2[9]);
Vector2** getPosition(Vector2* ma)
{
	
	//前左 前右
	pos[0].x = ma->x - 1;
	pos[0].y = ma->y - 2;
	pos[1].x = ma->x + 1;
	pos[1].y = ma->y - 2;

	//后左 后右
	pos[2].x = ma->x - 1;
	pos[2].y = ma->y + 2;
	pos[3].x = ma->x + 1;
	pos[3].y = ma->y + 2;
	//左前 左后
	pos[4].x = ma->x - 2;
	pos[4].y = ma->y - 1;
	pos[5].x = ma->x - 2;
	pos[5].y = ma->y + 1;
	//右前 右后
	pos[6].x = ma->x + 2;
	pos[6].y = ma->y - 1;
	pos[7].x = ma->x + 2;
	pos[7].y = ma->y + 1;

	pos[8] = *ma;	
	return &pos;
}

不知道为什么，求助大佬。