def f(x, N):
    v = 0
    inv = pow(N - x + 1, mod - 2, mod)
    for i in range(1, N + 1):
        v += (min(i, x, N - x + 1, N - i + 1) * inv) ** 2
        v %= mod
    return v

H, W, A, B = map(int, input().split())
mod = 998244353
ans = 2 * A * B - f(A, H) * f(B, W)
print(ans % mod)