def comb_lut(N, MOD):
   F = [1]*(N+1)
   for i in range(N):
      F[i+1] = F[i] * (i+1) % MOD
   InvF = [1]*(N+1)
   InvF[N] = pow(F[N], -1, MOD)
   for i in range(N)[::-1]:
      InvF[i] = InvF[i+1] * (i+1) % MOD

   def comb(n, r):
      assert 0 <= n <= N and 0 <= r
      if 0 <= r <= n: return F[n] * InvF[r] % MOD * InvF[n-r] % MOD
      else: return 0

   return comb

MOD = 998_244_353
N = int(input())
A = list(map(int, input().split()))

comb = comb_lut(N + max(A), MOD)

ans = 1
for q, a in enumerate(A, 1):
   term = comb(q+a-1, q)
   ans += term
   ans %= MOD

print(ans)