H, W, A, B = map(int, input().split())

MOD = 998244353

def inverse(n, d):
    return n * pow(d, -1, MOD) % MOD

sumH = 0
for i in range(1, A+1):
    if i < A:
        if A*2-i > H:
            continue
        sumH += (H-A+1-(A-i))*2*i%MOD
        sumH %= MOD
    else:
        sumH += (H-A+1)*i%MOD
        sumH %= MOD
sumH = inverse(sumH, (H-A+1)**2%MOD)
sumW = 0
for i in range(1, B+1):
    if i < B:
        if B*2-i > W:
            continue
        sumW += (W-B+1-(B-i))*2*i%MOD
        sumW %= MOD
    else:
        sumW += (W-B+1)*i%MOD
        sumW %= MOD
sumW = inverse(sumW, (W-B+1)**2%MOD)

print((A*B*2-sumH*sumW)%MOD)