modulus = 998244353

def main():
	x,y,z,w=map(int,input().split())	
	n = x-z+y-w
	f = fact(n-1)
	b1 = bin(x,x-z-1) if z == 0 else bin(x,x-z)
	b2 = bin(y,y-w-1) if w == 0 else bin(y,y-w)
	ans = (f*b1*b2) % modulus
	print(ans)

def fact(n):
	p = 1
	for k in range(1,n+1):
		p *= k
		p %= modulus
	return p

def bin(n,k):
	a = fact(n)
	b = fact(n-k)
	c = fact(k)
	bc = pow(b*c,-1,modulus)
	ans = a*bc % modulus
	return ans

if __name__ == "__main__":
	main()