#define MD 998244353
ll@H,@W,@A,@B;Mint a=H*W,S=(H-A+1)*(W-B+1),t,u;a=H*W;rep(i,H){u=0;rep(j,W){t=(1-(max(min(i,H-A)-max(i-A,-1),0)*max(min(j,W-B)-max(j-B,-1),0))/S)**2;if(B<=j<W-B)u+=t*(W-2B),j=W-B-1;else u+=t;}if(A<=i<H-A)a-=u*(H-2A),i=H-A-1;else a-=u;}wt(a);