x,y,z,w = map(int,input().split())
nmax = x+y; mod = 998244353; fa = [1]*(nmax+1); fi = [1]*(nmax+1)
for i in range(1,nmax): fa[i+1] = fa[i]*(i+1)%mod
fi[nmax] = pow(fa[nmax],mod-2,mod)
for i in range(nmax,0,-1): fi[i-1] = fi[i]*i%mod
def cmb(n,r): return fa[n]*fi[n-r]%mod*fi[r]%mod if 0<=r<=n else 0
if z==0: x,y,z,w = y,x,w,z
print(cmb(x,z)*y*fa[x+y-z-1]%mod)