#include <iostream>
#include <string>
using namespace std;
long long arr[30][30];

int main()
{
	int x, y, a, b;
	cin >> x >> y >> a >> b;

	for (int t = 0; t < 30; t++)
	{
		arr[0][t] = 1;
		arr[t][0] = 1;
	}
	if (a - 2 >= 0 && b - 1 >= 0) arr[a - 2][b - 1] = -1;
	if (a - 2 >= 0) arr[a - 2][b + 1] = -1;
	if (b - 1 >= 0) arr[a + 2][b - 1] = -1;
	arr[a + 2][b + 1] = -1;
	if (b - 2 >= 0) arr[a + 1][b - 2] = -1;
	arr[a + 1][b + 2] = -1;
	if (a - 1 >= 0) arr[a - 1][b + 2] = -1;
	if (a - 1 >= 0 && b - 2 >= 0) arr[a - 1][b - 2] = -1;
	arr[a][b] = -1;
	int i, k;
	for (i = 1; i <= x; i++)
	{
		for (k = 1; k <= y; k++)
		{
			if (arr[i][k] == -1) continue;
			arr[i][k] = arr[i - 1][k] + arr[i][k - 1];
			if (arr[i - 1][k] == -1) arr[i][k] += 1;
			if (arr[i][k - 1] == -1) arr[i][k] += 1;
		}
	}
	cout << arr[x][y];
	return 0;
}