MOD = 998244353


def my_factorial(a):
	ret = 1
	for i in range(1, a+1):
		ret *= i
		ret %= MOD

	return ret


def comb(a, b):
	ret = my_factorial(a)
	d = my_factorial(b) * my_factorial(a-b)
	d %= MOD

	ret = my_factorial(a) * pow(d, MOD-2, MOD)
	return ret % MOD


X, Y, Z, W = map(int, input().split())

if Z == 0:
	ans = comb(Y, Y-W) * X * my_factorial(X+Y-W-1)
else:
	ans = comb(X, X-Z) * Y * my_factorial(X+Y-Z-1)
print(ans % MOD)