mod = 998244353
n = 10**7
fact = [1 for i in range(n+1)]
fact_inv = [1 for i in range(n+1)]
for i in range(1,n+1):
  fact[i] = fact[i-1]*i % mod
fact_inv[-1] = pow(fact[-1],mod-2,mod)
for i in range(n,0,-1):
  fact_inv[i-1] = fact_inv[i]*i % mod
def binom(n,r):
  if n < r or n < 0 or r < 0:
    return 0
  res = fact_inv[n-r] * fact_inv[r] % mod
  res *= fact[n]
  res %= mod
  return res

N = int(input())
A = list(map(int,input().split()))

ans = 0
for i in range(1,N):
  a,aa = A[i-1],A[i]
  ans += binom(a+i,i) - binom(aa+i,i)
  ans %= mod
ans += binom(A[-1]+N,N)
print(ans % mod)