N=int(input())
A=list(map(int,input().split()))
u=[1]*(10**6)
mod=998244353
u2=[1]*(10**6)
for i in range(1,10**6):
  u[i]=u[i-1]*i
  u2[i]=pow(u[i],-1,mod)
  u[i]%=mod
def ncm(x,y):
  if y<0:
    return 0
  ans=u[x]*u2[x-y]
  ans%=mod
  ans*=u2[y]
  ans%=mod
  return ans
result=1
for i in range(N):
  x=A[i]
  result+=ncm(x+i+1,x)-1-(ncm(x+i,i)-1)
  result%=mod
print(result)