#include <bits/stdc++.h>

using ll = long long;
using std::cin;
using std::cout;
using std::endl;

std::mt19937 rnd(std::chrono::steady_clock::now().time_since_epoch().count());
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return 1;
    }
    return 0;
}

constexpr int inf = (int)1e9 + 7;
constexpr long long INF = 1LL << 60;

template <int mod>
struct ModInt
{
    int x;

    ModInt() : x(0) {}

    ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

    ModInt &operator+=(const ModInt &p)
    {
        if ((x += p.x) >= mod)
            x -= mod;
        return *this;
    }

    ModInt &operator-=(const ModInt &p)
    {
        if ((x += mod - p.x) >= mod)
            x -= mod;
        return *this;
    }

    ModInt &operator*=(const ModInt &p)
    {
        x = (int)(1LL * x * p.x % mod);
        return *this;
    }

    ModInt &operator/=(const ModInt &p)
    {
        *this *= p.inverse();
        return *this;
    }

    ModInt operator-() const { return ModInt(-x); }

    ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

    ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

    ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

    ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

    bool operator==(const ModInt &p) const { return x == p.x; }

    bool operator!=(const ModInt &p) const { return x != p.x; }

    ModInt inverse() const
    {
        int a = x, b = mod, u = 1, v = 0, t;
        while (b > 0)
        {
            t = a / b;
            std::swap(a -= t * b, b);
            std::swap(u -= t * v, v);
        }
        return ModInt(u);
    }

    ModInt pow(int64_t n) const
    {
        ModInt ret(1), mul(x);
        while (n > 0)
        {
            if (n & 1)
                ret *= mul;
            mul *= mul;
            n >>= 1;
        }
        return ret;
    }

    friend std::ostream &operator<<(std::ostream &os, const ModInt &p)
    {
        return os << p.x;
    }

    friend std::istream &operator>>(std::istream &is, ModInt &a)
    {
        int64_t t;
        is >> t;
        a = ModInt<mod>(t);
        return (is);
    }

    static int get_mod() { return mod; }
};

constexpr int mod = 998244353;
using mint = ModInt<mod>;

void solve()
{
    int H, W, A, B;
    cin >> H >> W >> A >> B;
    std::vector<mint> dupH(A + 2), dupW(B + 2);
    {
        mint p = mint(1) / mint(H - A + 1);
        for (int i = 0; i <= H - A; i++)
        {
            {
                int l = std::max(0, (i + A) - (H - A));
                int r = A;
                dupH[l] += p * p;
                dupH[r + 1] -= p * p;
            }
            {
                int l = std::max(0, A - i);
                int r = A - 1;
                dupH[l] += p * p;
                dupH[r + 1] -= p * p;
            }
        }
        for (int i = 0; i < (int)dupH.size() - 1; i++)
        {
            dupH[i + 1] += dupH[i];
        }
    }
    {
        mint p = mint(1) / mint(W - B + 1);
        for (int i = 0; i <= W - B; i++)
        {
            {
                int l = std::max(0, (i + B) - (W - B));
                int r = B;
                dupW[l] += p * p;
                dupW[r + 1] -= p * p;
            }
            {
                int l = std::max(0, B - i);
                int r = B - 1;
                dupW[l] += p * p;
                dupW[r + 1] -= p * p;
            }
        }
        for (int i = 0; i < (int)dupW.size() - 1; i++)
        {
            dupW[i + 1] += dupW[i];
        }
    }
    mint ans = mint(A) * B * 2;
    mint h_sum = 0, w_sum = 0;
    for (int i = 0; i <= A; i++)
    {
        h_sum += dupH[i] * i;
    }
    for (int i = 0; i <= B; i++)
    {
        w_sum += dupW[i] * i;
    }
    ans -= h_sum * w_sum;
    cout << ans << "\n";
}

int main()
{
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    int kkt = 1;
    // cin >> kkt;
    while (kkt--)
    {
        solve();
    }
}