H,W,A,B=map(int, input().split())
mod=998244353
def xgcd(a, b):
    x0, y0, x1, y1 = 1, 0, 0, 1
    while b != 0:
        q, a, b = a // b, b, a % b
        x0, x1 = x1, x0 - q * x1
        y0, y1 = y1, y0 - q * y1
    return a, x0, y0

def modinv(a, m):
    g, x, y = xgcd(a, m)
    if g != 1:
        raise Exception('modular inverse does not exist')
    else:
        return x % m


p=0
for i in range(1,W+1):
  c=min(min(abs(1-i),abs(W-i))+1,B) 
  p+=c**2

q=0
for i in range(1,H+1):
  c=min(min(abs(1-i),abs(H-i))+1,A) 
  q+=c**2

c=(H-A+1)*(W-B+1)
cc=c*c%mod
ans=2*A*B-p*q*modinv(cc,mod)
print(ans%mod)