#include<stdio.h>

int a[100][100];
int b[100][100];
int dir[8][2] = { {1,2},{2,1},{-1,2},{-1,-2},{1,-2},{2,-1},{-2,1},{-2,-1} };
int bx, by, hx, hy,tx,ty;
int main()
{
	scanf("%d%d%d%d", &bx, &by, &hx, &hy);
	hx += 2;
	hy += 2;
	bx += 2;
	by += 2;
	b[hx][hy] = 1;
	a[0][0] = 0;
	for (int i = 0; i < 8; i++)
	{
		tx = hx + dir[i][0];
		ty = hy + dir[i][1];
		b[tx][ty] = 1;
	}
	for (int i = 3; i <= bx; i++)
	{
		if(b[i][2]==0)
		a[i][2] = 1;
	}
	for (int i = 3; i <= by; i++)
	{
		if(b[2][i]==0)
		a[2][i] = 1;
	}
	for (int i = 3; i <= bx; i++)
	{
		for (int j = 3; j <= by; j++)
		{
			if(b[i][j]==0)
			{
				a[i][j] = a[i - 1][j] + a[i][j - 1];
			}
		}
	}
	printf("%d", a[bx][by]);
	return 0;
}