#include #include #include #include #include #include #include #include #include #include #include #include #include #include #define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl; #define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl; template inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; } template inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; } using namespace std; typedef long long ll; template vector> vec2d(int n, int m, T v){ return vector>(n, vector(m, v)); } template vector>> vec3d(int n, int m, int k, T v){ return vector>>(n, vector>(m, vector(k, v))); } template void print_vector(vector v, char delimiter=' '){ if(v.empty()) { cout << endl; return; } for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter; cout << v.back() << endl; } using mint = atcoder::modint998244353; ostream& operator<<(ostream& os, const mint& m){ os << m.val(); return os; } int main(){ ios::sync_with_stdio(false); cin.tie(0); cout << setprecision(10) << fixed; int h, w, n, k; cin >> h >> w >> n >> k; auto make_v = [&](int len){ vector ans(k+1); if(len >= 2*k+1){ for(int x = 1; x < k; x++) ans[x] = 2; ans[k] = len-2*(k-1); return ans; } int rem = len; for(int i = 0; i < len; i++){ int l = max(0, i-k+1); int r = min(i, h-k); ans[r-l+1]++; } return ans; }; vector cx = make_v(h); vector cy = make_v(w); // print_vector(cx); mint ans = 0; mint area = mint(h-k+1)*mint(w-k+1); for(int x = 1; x <= k; x++){ for(int y = 1; y <= k; y++){ mint ok_area = mint(x)*mint(y); mint rem_area = area-ok_area; mint p_ng = rem_area/area; mint p_all_ng = p_ng.pow(n); ans += (1-p_all_ng)*cx[x]*cy[y]; } } cout << ans << endl; }