def nPr(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    return g1[n] * g2[n-r] % mod

def nCr(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return (g1[n] * g2[r] % mod) * g2[n-r] % mod

MOD = 998244353
X, Y, Z, W = map(int, input().split())
N = X+Y

g1 = [1, 1] # 元テーブル
g2 = [1, 1] #逆元テーブル
inverse = [0, 1] #逆元テーブル計算用テーブル
fact = [1, 1]

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % MOD )
    inverse.append( ( -inverse[MOD % i] * (MOD//i) ) % MOD )
    g2.append( (g2[-1] * inverse[-1]) % MOD )
    fact.append( (fact[-1] * i) % MOD )

ans = 1
if Z<W:
    ans *= nCr(Y, W, MOD)
    ans %= MOD
    ans *= (fact[X+Y-W] - fact[X+Y-W-1]*nCr(Y-W, 1, MOD)%MOD) % MOD
    ans %= MOD
else:
    ans *= nCr(X, Z, MOD)
    ans %= MOD
    ans *= (fact[X+Y-Z] - fact[X+Y-Z-1]*nCr(X-Z, 1, MOD)%MOD) % MOD
    ans %= MOD

print(ans)