package main

import . "fmt"
import . "math/big"

func main() {
	const Mod = 998244353

	var x, y, z, w int
	Scan(&x, &y, &z, &w)

	m := x+y
	n := make([]int, m+1)
	n[0] = 1
	for i := range n[1:] {
		n[i+1] = n[i]*(i+1)%Mod
	}
	d := make([]int, m+1)
	d[m] = int(new(Int).ModInverse(NewInt(int64(n[m])), NewInt(Mod)).Int64())
	for i := range d[1:] {
		j := m - i
		d[j-1] = d[j]*j%Mod
	}

	// なんかサンプルは合うが、理屈わかってない
	e := (x - z) + (y - w)
	ans := (n[x]*d[z]%Mod)*
		(n[y]*d[w]%Mod)%Mod*
		(n[e-1]*d[x-max(1,z)]%Mod*d[y-max(1,w)]%Mod)%Mod
	Println(ans)
}