x,y,z,w=map(int, input().split())
mod=998244353;n=10**6+100
inv_t=[0]+[1]
for i in range(2,n):
  inv_t+=[inv_t[mod%i]*(mod-int(mod/i))%mod]

kai=[1,1]
rev_kai=[1,inv_t[1]]
for i in range(2,n):
  kai.append(kai[-1]*i%mod)
  rev_kai.append(rev_kai[-1]*inv_t[i]%mod)

def cmb(n,r):
  return kai[n]*rev_kai[r]*rev_kai[n-r]%mod

if z==0:
  ans=x*cmb(y,w)
  z+=1
else:
  ans=y*cmb(x,z)
  w+=1

c=x+y-z-w
for i in range(1,c+1):
  ans*=i
  ans%=mod 
print(ans)