#include namespace { #pragma GCC diagnostic ignored "-Wunused-function" #include #pragma GCC diagnostic warning "-Wunused-function" using namespace std; using namespace atcoder; #define rep(i,n) for(int i = 0; i < (int)(n); i++) #define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--) #define all(x) begin(x), end(x) #define rall(x) rbegin(x), rend(x) template bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; } template bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; } using ll = long long; using P = pair; using VI = vector; using VVI = vector; using VL = vector; using VVL = vector; using mint = modint998244353; } int main() { ios::sync_with_stdio(false); cin.tie(0); int h, w, a, b; cin >> h >> w >> a >> b; mint x1, x2, y1, y2; rep(i, h) { int cnt = a - max(a - i - 1, 0) - max(i + a - h, 0); x1 += mint(cnt); x2 += mint(cnt).pow(2); } rep(j, w) { int cnt = b - max(b - j - 1, 0) - max(j + b - w, 0); y1 += mint(cnt); y2 += mint(cnt).pow(2); } mint ans1 = (x1 * y1) / mint(ll(h - a + 1) * (w - b + 1)); mint ans2 = (x2 * y2) / mint(ll(h - a + 1) * (w - b + 1)).pow(2); mint ans = 2 * ans1 - ans2; cout << ans.val() << '\n'; }