m, n, m1, n1 = [int(x) for x in input().split(' ')]


def ma(L):
    if L == []:
        return 0
    else:
        return [ma(L[1:]) for i in range(L[0])]


y = ma([21, 21])
y[0][0] = 1
x = ma([21, 21])
x[m1][n1] = 1
for i in [-2, -1, 1, 2]:
    for j in [-2, -1, 1, 2]:
        if i != j and i + j != 0:
             x[m1 + i][n1 + j] = 1

for i in range(m + 1):
    for j in range(n + 1):
        if x[i][j] == 0:
            if (i == 0 and j == 0):
                pass
            else:
                y[i][j] = y[i - 1][j] + y[i][j - 1]

print(y[m][n])