X, Y, Z, W = map(int, input().split())
MOD = 998244353

if max(Z, W) == Z:
    a = X
    b = Y
    c = Z
else:
    a = Y
    b = X
    c = W    
    
s = X + Y - c - 1
t = 1
for i in range(1, s+1):
    t = t * i % MOD
t = t * b % MOD

def factorial_inverse(n, mod):
    fac = [1] * (n+1)
    inv = [1] * (n+1)
    finv = [1] * (n+1)
    
    for i in range(2, n+1):
        fac[i] = fac[i-1] * i % mod
        inv[i] = mod - inv[mod%i] * (mod//i) % mod
        finv[i] = finv[i-1] * inv[i] % mod
        
    return fac, finv


fac, finv = factorial_inverse(a, MOD)

d = fac[a] * (finv[c] * finv[a - c] % MOD) % MOD
ans = t * d % MOD
print(ans)