import sys
input = sys.stdin.readline


def comb_preprocess(n):
    fact = [1] * (n+1)
    fact_inv = [1] * (n+1)
    for i in range(1, n+1):
        fact[i] = i * fact[i-1] % mod
    fact_inv[n] = pow(fact[n], mod-2, mod)
    for i in range(1, n+1)[::-1]:
        fact_inv[i-1] = i * fact_inv[i] % mod

    def comb(n, k):
        if k < 0 or n < k:
            return 0
        return fact[n] * fact_inv[k] % mod * fact_inv[n-k] % mod

    return fact, fact_inv, comb


mod = 998244353
X, Y, Z, W = map(int, input().split())
human = X-Z
wolf = Y-W
fact, fact_inv, comb = comb_preprocess(X+Y)
ans = comb(X, human) * comb(Y, wolf) * (human if Z ==
                                        0 else wolf) * fact[human+wolf-1] % mod
print(ans)