MOD = 998244353

def perm(n, k):
    res = 1
    for i in range(k):
        res = res * (n - i) % MOD
    return res

def comb(n, k):
    a1 = 1
    a2 = 1
    for i in range(k):
        a1 = a1 * (n - i) % MOD
        a2 = a2 * (i + 1) % MOD
    return a1 * pow(a2, MOD - 2, MOD)

x, y, z, w = map(int, input().split())
p = x - z - (z == 0)
q = y - w - (w == 0)

answer = 1
answer = answer * perm(x, x - z) % MOD
answer = answer * perm(y, y - w) % MOD
answer = answer * comb(p + q, p) % MOD

print(answer)