class ModComb:
    def __init__(self, n: int, mod: int):
        fact = [0] * (n+1)
        fact[0] = 1
        for i in range(1, n+1):
            fact[i] = i * fact[i-1] % mod

        ifact = [0] * (n+1)
        ifact[n] = pow(fact[n], mod-2, mod)
        for i in range(n, 0, -1):
            ifact[i-1] = ifact[i] * i % mod
        self.fact = fact
        self.ifact = ifact
        self.mod = mod

    def __call__(self, n: int, k: int) -> int:
        if n < 0 or k > n: return 0
        return (self.fact[n] * self.ifact[k] % self.mod) * self.ifact[n-k] % self.mod


MOD = 998244353
X, Y, Z, W = map(int, input().split())
comb = ModComb(X+Y, MOD)


def solve():
    t = X + Y - (Z + W)

    fact = comb.fact
    if Z == 0:
        return X * fact[t-1] * comb(Y, W) % MOD
    elif W == 0:
        return Y * fact[t-1] * comb(X, Z) % MOD

    assert False


ans = solve()
print(ans)