MOD = 998244353
X, Y, Z, W = map(int, input().split())
if Z == 0:
    X, Y, Z, W = Y, X, W, Z

N = X + Y
fact = [1]*(N+1)
rfact = [1]*(N+1)
r = 1
for i in range(1, N+1):
    fact[i] = r = r * i % MOD
rfact[N] = r = pow(fact[N], MOD-2, MOD)
for i in range(N, 0, -1):
    rfact[i-1] = r = r * i % MOD

# nCk (mod MOD) を求める
def comb(n, k):
    return fact[n] * rfact[k] * rfact[n-k] % MOD

ans = comb(X - Z + Y - 1, X - Z)
ans *= fact[X] * rfact[Z]
ans %= MOD
ans *= fact[Y]
ans %= MOD
print(ans)