H,W,A,B=map(int,input().split())
M=998244353
c=[0]*(H+2)
for i in range(H-A+1):
  c[i]+=1
  c[i+A]-=1
for i in range(1,H):
  c[i]+=c[i-1]
ex=sum(c[i]**2 for i in range(H))*pow(pow(H-A+1,M-2,M),2,M)%M
c=[0]*(W+2)
for i in range(W-B+1):
  c[i]+=1
  c[i+B]-=1
for i in range(1,W):
  c[i]+=c[i-1]
ey=sum(c[i]**2 for i in range(W))*pow(pow(W-B+1,M-2,M),2,M)%M
e=ex*ey%M
e=A*B+A*B-e
e%=M
print(e)