class CP:
    def __init__(self, N):
        self.fact = [1]
        self.fact_inv = [1]
        for i in range(1, N+1):
            self.fact.append((self.fact[-1]*i)%MOD)
            self.fact_inv.append(pow(self.fact[-1], -1, MOD))
    def C(self, N, K):
        if N >= K:
            return self.fact[N]*self.fact_inv[K]%MOD*self.fact_inv[N-K]%MOD
        else:
            return 0
    def P(self, N, K):
        if N >= K:
            return self.fact[N]*self.fact_inv[N-K]%MOD
        else:
            return 0

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

MOD = 998244353

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

if Y == 0:
    exit(print(1))

P = [1]
for i in range(1, 10**6+1):
    P.append(P[-1]*i%MOD)

diffX = X-Z
cp = CP(10**6)
ans = cp.C(diffX+Y-1, diffX)
ans *= cp.C(X, diffX)
ans %= MOD
ans *= (P[diffX]*P[Y])%MOD
ans %= MOD

print(ans)