a,b,c,d=map(int,input().split())
M=998244353
if c>d:
	a,b=b,a
	c,d=d,c 
x=a
y=b-d
ans=x
for i in range(y+1,x+y):
	ans=(ans*i)%M
ans2=1
for i in range(d+1,b+1):
	ans=(ans*i)%M 
print(ans)