mod = 998244353

X, Y, Z, W = map(int, input().split())
if Z == 0:
    X, Y = Y, X
    Z, W = W, Z
fact = [1]
for i in range(600005):
    fact.append((fact[-1] * (i + 1)) % mod)

ans = (fact[X] * ((pow(fact[X - Z], mod - 2, mod)
                   * pow(fact[Z], mod - 2, mod)) % mod)) % mod
ans = (ans * Y) % mod
ans = (ans * fact[X + Y - Z - 1]) % mod
print(ans)