# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
from collections import defaultdict as dd
S = input
R = range
P = print
def I(): return int(S())
def M(): return map(int, S().split())
def L(): return list(M())
def O(): return list(map(int, open(0).read().split()))
def yn(b): print("Yes" if b else "No")
biga = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
smaa = "abcdefghijklmnopqrstuvwxyz"
def acc(a):
	b = [0]
	for i in a:
		b.append(b[-1] + i)
	return b


class Comb:
	def __init__(self, N, mod = 1000000007):
		self.n = N
		self.mod = mod
		self.fac = [0] * (self.n + 1)
		self.invf = [0] * (self.n + 1)
		self.inv = [0] * (self.n + 1)
		self.fac[0] = 1
		self.fac[1] = 1
		self.invf[0] = 1
		self.invf[1] = 1
		self.inv[1] = 1
		for i in range(2, self.n + 1):
			self.fac[i] = self.fac[i - 1] * i % self.mod
			self.inv[i] = self.mod - self.inv[self.mod % i] * (self.mod // i) % self.mod
			self.invf[i] = self.invf[i - 1] * self.inv[i] % self.mod
	def F(self, N):
		return self.fac[N]
	def C(self, N, K):
		return self.invf[K] * self.invf[N - K] % self.mod * self.fac[N] % self.mod
	def P(self, N, K):
		return self.invf[N - K] * self.fac[N] % self.mod
	def H(self, N, K):
		return self.invf[K] * self.invf[N - 1] % self.mod * self.fac[N + K - 1] % self.mod

N = int(input())
A = L() + [-1]
c = Comb(10 ** 6, 998244353)
mod = 998244353
ans = 0
for i in range(N):
	for j in range(A[i + 1] + 1, A[i] + 1):
		ans += c.C(i + j, i)
print(ans % mod)