def Map():
  return list(map(int,input().split()))

mod = 998244353

H,W,A,B = Map()

p = 0
pp = 0
for h in range(H):
  l = max(0,h+1-A)
  r = min(h,H - A)
  x = r - l + 1
  p += x
  pp += pow(x,2,mod)
  p %= mod
  pp %= mod

q = 0
qq = 0
for w in range(W):
  l = max(0,w+1-B)
  r = min(w,W - B)
  x = r - l + 1
  q += x
  qq += pow(x,2,mod)
  q %= mod
  qq %= mod

n = (H - A + 1) * (W - B + 1) % mod
m = pow(n,2,mod)

C = 2*p*q*n
C %= mod
C -= pp*qq
C %= mod
C *= pow(m,-1,mod)
C %= mod
print(C)