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 Cumprod(m int, a []int) {
	n := len(a)
	for i := 0; i < n-1; i++ {
		a[i+1] *= a[i]
		a[i+1] %= m
	}
}

func Fact(m, n int) []int {
	f := Iota(n)
	f[0] = 1
	Cumprod(m, f)
	return f
}

func InvTable(m, n int) []int {
	f := make([]int, n)
	f[1] = 1
	for i := 2; i < n; i++ {
		q, r := Divmod(m, i)
		f[i] = m - q*f[r]%m
	}
	return f
}

func InvFact(m, n int) []int {
	f := InvTable(m, n)
	f[0] = 1
	Cumprod(m, f)
	return f
}

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
}

type Tables struct {
	F, Fi, Inv []int
	m          int
}

func (
	t *Tables,
) Init(m, n int) *Tables {
	inv := InvTable(m, n)
	f := make([]int, n)
	fi := make([]int, n)
	f[0] = 1
	fi[0] = 1
	for i := 1; i < n; i++ {
		f[i] = f[i-1] * i % m
		fi[i] = fi[i-1] * inv[i] % m
	}
	*t = Tables{
		F:   f,
		Fi:  fi,
		Inv: inv,
		m:   m,
	}
	return t
}

func (t *Tables) P(n, k int) int {
	if k < 0 || n < k {
		return 0
	}
	return t.F[n] * t.Fi[n-k] % t.m
}

func (t *Tables) C(n, k int) int {
	if k < 0 {
		return 0
	}
	return t.P(n, k) * t.Fi[k] % t.m
}

func (t *Tables) H(n, k int) int {
	return t.C(n-1+k, k)
}

func (t *Tables) IP(n, k int) int {
	Assert(0 <= k && k <= n)
	return t.Fi[n] * t.F[n-k] % t.m
}

func (t *Tables) IC(n, k int) int {
	return t.IP(n, k) * t.F[k] % t.m
}

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

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

	const m int = 998244353
	t := new(Tables).Init(m, 1<<20)
	ans := t.F[x+y-z-w]
	ans *= t.C(x, z)
	ans %= m
	ans *= t.C(y, w)
	ans %= m
	Out(ans)
}