H, W, A, B = map(int, input().split())
mod = 998244353
alpha, beta = pow(H-A+1, mod-2, mod), pow(W-B+1, mod-2, mod)
p = [0] * H
q = [0] * W
for i in range(H):
    l = max(0, i-A+1)
    r = min(H-1, i+A-1)
    p[i] = (r-l-A+2)*alpha%mod
for j in range(W):
    l = max(0, j-B+1)
    r = min(W-1, j+B-1)
    q[j] = (r-l-B+2)*beta%mod

sp, sq = 0, 0
sp2, sq2 = 0, 0
for v in p:
    sp += v
    sp2 += v*v
    sp = sp%mod
    sp2 = sp2%mod
for v in q:
    sq += v
    sq2 += v*v
    sq = sq%mod
    sq2 = sq2%mod
print((2*sp*sq - sp2*sq2)%mod)