#define MD 998244353
Comb<Mint>c;
ll@x,@y;
if(x>4000||y>4000)exit(1);
Mint r;
rep(z,min(x,y)+1){
	rep(w,z+1){
		r+=c.Multinomial(x-z,y-z,w)*c.pw2(w);
	}
}
wt(r);