MOD = 998244353
X,Y,Z,W = map(int,input().split())
A = list(range(X+Y+1))
A[0] = 1
for i in range(2,X+Y+1):
    A[i] = (A[i-1]*i)%MOD
B = list(range(X+Y+1))
B[0] = 1
B[X+Y] = pow(A[X+Y],MOD-2,MOD)
for i in range(X+Y-1,0,-1):
    B[i] = (B[i+1]*(i+1))%MOD
ans = 0
if Z==0:
    ans = (X*A[X+Y-W-1]*A[Y]*B[Y-W]*B[W])%MOD
else:
    ans = (Y*A[X+Y-Z-1]*A[X]*B[X-Z]*B[Z])%MOD
print(ans)