x,y,z,w = map(int,input().split())

human = x-z
wolf = y-w
mod = 998244353
ans = 1
class comb():
    def __init__(self,n,mod):
        self.fact = [0] * (n+1)
        self.fact_inv = [0] * (n+1)
        self.mod = mod

        self.fact[1] = 1
        self.fact_inv[1] = pow(1,mod-2,mod)
        self.fact[0] = 1
        self.fact_inv[0] = 1

        for i in range(2,n+1):
            self.fact[i] = (self.fact[i-1] * i) % mod
            self.fact_inv[i] = (self.fact_inv[i-1] * pow(i,mod-2,mod)) % mod
        
    def ncr(self,n,r):
        return (self.fact[n] * self.fact_inv[r] * self.fact_inv[n-r]) % self.mod
c = comb(3*10**5+10,mod)
if w == 0:
    human,wolf = wolf,human
    z,w=w,z
    x,y=y,x
if z == 0:
    human -= 1
    ans *= c.ncr(human+wolf,min(human,wolf))
    ans *= c.ncr(x,human+1)
    ans *= c.ncr(y,wolf)
    ans *=c.fact[human+1]
    ans %= mod
    ans *= c.fact[wolf]
    ans %= mod
print(ans)