#include using namespace std; #define all(v) (v).begin(),(v).end() #define pb(a) push_back(a) #define rep(i, n) for(int i=0;i struct Modint { long long val; constexpr Modint(long long v = 0) noexcept : val(v % MOD) { if (val < 0) val += MOD; } constexpr int mod() const { return MOD; } constexpr long long value() const { return val; } constexpr Modint operator - () const noexcept { return val ? MOD - val : 0; } constexpr Modint operator + (const Modint& r) const noexcept { return Modint(*this) += r; } constexpr Modint operator - (const Modint& r) const noexcept { return Modint(*this) -= r; } constexpr Modint operator * (const Modint& r) const noexcept { return Modint(*this) *= r; } constexpr Modint operator / (const Modint& r) const noexcept { return Modint(*this) /= r; } constexpr Modint& operator += (const Modint& r) noexcept { val += r.val; if (val >= MOD) val -= MOD; return *this; } constexpr Modint& operator -= (const Modint& r) noexcept { val -= r.val; if (val < 0) val += MOD; return *this; } constexpr Modint& operator *= (const Modint& r) noexcept { val = val * r.val % MOD; return *this; } constexpr Modint& operator /= (const Modint& r) noexcept { long long a = r.val, b = MOD, u = 1, v = 0; while (b) { long long t = a / b; a -= t * b, swap(a, b); u -= t * v, swap(u, v); } val = val * u % MOD; if (val < 0) val += MOD; return *this; } constexpr bool operator == (const Modint& r) const noexcept { return this->val == r.val; } constexpr bool operator != (const Modint& r) const noexcept { return this->val != r.val; } friend constexpr istream& operator >> (istream& is, Modint& x) noexcept { is >> x.val; x.val %= MOD; if (x.val < 0) x.val += MOD; return is; } friend constexpr ostream& operator << (ostream& os, const Modint& x) noexcept { return os << x.val; } constexpr Modint pow(long long n) noexcept { if (n == 0) return 1; if (n < 0) return this->pow(-n).inv(); Modint ret = pow(n >> 1); ret *= ret; if (n & 1) ret *= *this; return ret; } constexpr Modint inv() noexcept { long long a = this->val, b = MOD, u = 1, v = 0; while (b) { long long t = a / b; a -= t * b, swap(a, b); u -= t * v, swap(u, v); } return Modint(u); } }; const int MOD = MOD998; using mint = Modint; int main() { cin.tie(0); ios::sync_with_stdio(false); ll h, w, a, b; cin >> h >> w >> a >> b; mint ans = mint(a * b) * mint(h - a + 1).pow(2) * mint(w - b + 1).pow(2) * mint(2); mint numa = 0; for(ll i = 1; i <= a; i ++) { if(i == a) { numa += mint(i) * mint(h - a * 2 + 1 + i); } else if(h - a * 2 + 1 + i > 0) { numa += mint(i) * mint(h - a * 2 + 1 + i) * mint(2); } } mint numb = 0; for(ll i = 1; i <= b; i ++) { if(i == b) { numb += mint(i) * mint(w - b * 2 + 1 + i); } else if(w - b * 2 + 1 + i > 0) { numb += mint(i) * mint(w - b * 2 + 1 + i) * mint(2); } } ans -= numa * numb; cout << ans / (mint(h - a + 1).pow(2) * mint(w - b + 1).pow(2)) << endl; return 0; }