x,y,z,w = map(int,input().split())
mod = 998244353

### for bigger prime 
N = x+y+5
fact = [1]*N
finv = [1]*N
 
for i in range(2,N):
    fact[i] = (fact[i-1]*i)%mod
finv[-1] = pow(fact[-1],mod-2,mod)
for i in range(1,N)[::-1]:
    finv[i-1] = (finv[i]*i)%mod

def nCr(n,r):
    if r > n:
        return 0
    else: 
        return fact[n]*finv[r]%mod*finv[n-r]%mod


if z:
    x,y = y,x
    z,w = w,z

## z = 0

ans = nCr(y,y-w) * nCr(x+y-z-w,x) * fact[y-w] * fact[x] % mod

for i in range(x-z,x+y-z-w):
    ans -= nCr(y,y-w) * nCr(i-1,x-1) * fact[y-w] * fact[x] % mod
    ans %= mod
print(ans)