import sys
input = sys.stdin.readline

mod=998244353

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

def calc(H,A):
    ANS=A*2*(H-A+1)*(H-A+1)

    kasanari=0

    for i in range(H-A+1):
        left=min(A,i)
        right=min(A,H-A-i)

        kasanari-=A

        kasanari+=(A+(A-left))*(left+1)*pow(2,mod-2,mod)
        kasanari+=(A+(A-right))*(right+1)*pow(2,mod-2,mod)
        #print(left,right)

    return kasanari*pow(H-A+1,mod-2,mod)*pow(H-A+1,mod-2,mod)%mod
        
x=calc(H,A)
y=calc(W,B)

print((A*B*2-x*y)%mod)