M = 5 * 10 ** 5 + 1
MOD = 998244353

f = [0 for _ in range(M)]
f_inv = [0 for _ in range(M)]
inv = [0 for _ in range(M)]

f[0], f[1] = 1, 1
f_inv[0], f_inv[1] = 1, 1
inv[1] = 1

for i in range(2, M):
    f[i] = (f[i-1] * i) % MOD
    inv[i] = MOD - inv[MOD % i] * (MOD // i) % MOD
    f_inv[i] = f_inv[i-1] * inv[i] % MOD


def C(n, k):
    if n < k:
        return 0
    elif n < 0 or k < 0:
        return 0
    return f[n]*(f_inv[k]*f_inv[n-k] % MOD) % MOD


def main():
    X, Y, Z, W = map(int, input().split())

    if Z == 0:
        X, Y = Y, X
        Z, W = W, Z

    assert W == 0

    ans = (C(X, X - Z) * C(Y, Y - W)) % MOD
    ans *= f[X + Y - Z - W] - f[X + Y - Z - W - 1] * (X - Z)
    ans %= MOD
    ans += MOD
    ans %= MOD

    print(ans)


main()