package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

func Assert(ok bool) {
	if !ok {
		panic("assertion failed")
	}
}

var sc = func() *bufio.Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	return sc
}()

func Str() string {
	sc.Scan()
	return sc.Text()
}

func Int() int {
	x, _ := strconv.Atoi(Str())
	return x
}

func Float() float64 {
	x, _ := strconv.ParseFloat(Str(), 64)
	return x
}

var wr = bufio.NewWriter(os.Stdout)

func Out(a ...interface{}) {
	fmt.Fprintln(wr, a...)
}

func Format(a []int) string {
	s := fmt.Sprint(a)
	return s[1 : len(s)-1]
}

func Chmin(a *int, b int) bool {
	if b < *a {
		*a = b
		return true
	}
	return false
}

func Chmax(a *int, b int) bool {
	if b > *a {
		*a = b
		return true
	}
	return false
}

func Max(a ...int) int {
	mx := a[0]
	for _, x := range a {
		if x > mx {
			mx = x
		}
	}
	return mx
}

func Min(a ...int) int {
	mn := a[0]
	for _, x := range a {
		if x < mn {
			mn = x
		}
	}
	return mn
}

func Sum(a ...int) int {
	s := 0
	for _, x := range a {
		s += x
	}
	return s
}

// truncated
func Divmod(a, b int) (int, int) {
	q := a / b
	r := a - q*b
	return q, r
}

func Lb(a []int, x int) int {
	n := len(a)
	f := func(i int) bool {
		return a[i] >= x
	}
	return sort.Search(n, f)
}

func Ub(a []int, x int) int {
	n := len(a)
	f := func(i int) bool {
		return a[i] > x
	}
	return sort.Search(n, f)
}

func main() {
	defer wr.Flush()
	t := 1
	// t := Int()
	for ; t > 0; t-- {
		Solve()
	}
}

func Iota(n int) []int {
	a := make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = i
	}
	return a
}

func Egcd(a, b int) (int, int, int) {
	if b == 0 {
		if a < 0 {
			return -a, -1, 0
		} else {
			return a, 1, 0
		}
	}
	q, r := Divmod(a, b)
	g, s, t := Egcd(b, r)
	return g, t, s - q*t
}

func Inv(m, a int) int {
	Assert(0 < a && a < m)
	g, x, _ := Egcd(a, m)
	Assert(g == 1)
	if x < 0 {
		x += m
	}
	return x
}

const Mod = 998_244_353

func Tables(n int) (f, fi, inv []int) {
	f = make([]int, n)
	fi = make([]int, n)
	inv = make([]int, n)
	f[0] = 1
	fi[0] = 1
	for i := 1; i < n; i++ {
		f[i] = f[i-1] * i % Mod
	}
	fi[n-1] = Inv(Mod, f[n-1])
	for i := n - 1; i > 0; i-- {
		fi[i-1] = fi[i] * i % Mod
		inv[i] = fi[i] * f[i-1] % Mod
	}
	return
}

var Fact, IFact, Invs []int

func InitTables(n int) {
	Fact, IFact, Invs = Tables(n)
}

func Perm(n, k int) int {
	if k < 0 || n < k {
		return 0
	}
	return Fact[n] * IFact[n-k] % Mod

}

func Choose(n, k int) int {
	if k < 0 {
		return 0
	}
	return Perm(n, k) * IFact[k] % Mod
}

func Solve() {
	x, y := Int(), Int()
	z, w := Int(), Int()

	Chmax(&z, 1)
	Chmax(&w, 1)

	InitTables(1 << 20)
	ans := Fact[x+y-z-w]
	ans *= Choose(x, z)
	ans %= Mod
	ans *= Choose(y, w)
	ans %= Mod
	Out(ans)
}