h, w, a, b = map(int, input().split())
n = h + w
mod = 10 ** 9 + 7
fun = [1] * (n + 1)
for i in range(1, n + 1):
    fun[i] = fun[i - 1] * i % mod
rev = [1] * (n + 1)
rev[n] = pow(fun[n], mod - 2, mod)
for i in range(n - 1, 0, -1):
    rev[i] = rev[i + 1] * (i + 1) % mod


def nCr(n, r):
    if r > n:
        return 0
    return fun[n] * rev[r] % mod * rev[n - r] % mod


ans = 0
i = h - a
j = b + 1
while i > 0 and j <= w:
    ans = (ans + nCr(i + j - 2, i - 1) * nCr(h + w - i - j, h - i) % mod) % mod
    i -= 1
    j += 1
print(ans)

a3176537fcd38f334936f7c8c28d2eb1eb929f1b
<mask token>

<mask token>


def nCr(n, r):
    if r > n:
        return 0
    return fun[n] * rev[r] % mod * rev[n - r] % mod


<mask token>

<mask token>
for i in range(1, n + 1):
    fun[i] = fun[i - 1] * i % mod
<mask token>
for i in range(n - 1, 0, -1):
    rev[i] = rev[i + 1] * (i + 1) % mod


def nCr(n, r):
    if r > n:
        return 0
    return fun[n] * rev[r] % mod * rev[n - r] % mod


<mask token>
while i > 0 and j <= w:
    ans = (ans + nCr(i + j - 2, i - 1) * nCr(h + w - i - j, h - i) % mod) % mod
    i -= 1
    j += 1
print(ans)

h, w, a, b = map(int, input().split())
n = h + w
mod = 10 ** 9 + 7
fun = [1] * (n + 1)
for i in range(1, n + 1):
    fun[i] = fun[i - 1] * i % mod
rev = [1] * (n + 1)
rev[n] = pow(fun[n], mod - 2, mod)
for i in range(n - 1, 0, -1):
    rev[i] = rev[i + 1] * (i + 1) % mod


def nCr(n, r):
    if r > n:
        return 0
    return fun[n] * rev[r] % mod * rev[n - r] % mod


ans = 0
i = h - a
j = b + 1
while i > 0 and j <= w:
    ans = (ans + nCr(i + j - 2, i - 1) * nCr(h + w - i - j, h - i) % mod) % mod
    i -= 1
    j += 1
print(ans)
