#define MD 998244353
Comb<Mint>c;
ll@x,@y;
if(x>4000||y>4000)exit(1);
Mint r;
rrep(z,min(x,y)+1){
	r*=x-z;
	r*=y-z;
	Mint s;
	rrep(w,z+1){
		s+=s;
		s+=c.fac((x-z)+(y-z)+w)*c.ifac(w);
	}
	r+=s;
}
wt(r*c.ifac(x)*c.ifac(y));