import sys
#sys.setrecursionlimit(10 ** 6)
INF = float('inf')
MOD = 998244353
from collections import defaultdict
def ceil(A,B):
    return -(-A//B)
def modinv(x):
    return pow(x,MOD-2,MOD)
def binomial_coefficients(n, k):
    numera = 1  # 分子
    denomi = 1  # 分母
    for i in range(k):
        numera *= n - i
        numera %= MOD
        denomi *= i + 1
        denomi %= MOD
    return numera * modinv(denomi) % MOD
#binomial_coefficients(n, k)…n_C_k
def solve():
    def II(): return int(sys.stdin.readline())
    def LI(): return list(map(int, sys.stdin.readline().split()))
    def LC(): return list(sys.stdin.readline().rstrip())
    def IC(): return [int(c) for c in sys.stdin.readline().rstrip()]
    def MI(): return map(int, sys.stdin.readline().split())
    X,Y,Z,W = MI()
    if(Z==0):
        D = X
        N = Y
        R = Y-W
    elif(W ==0):
        D = Y
        N = X
        R = X - Z
    Ans = 1
    for d in range(1,D+1):
        Ans*=d
        Ans%=MOD

    Ans *= binomial_coefficients(N, R)
    for r in range(R):
        Ans*=(D+r)
        Ans%=MOD

    print(Ans%MOD)
    return
solve()