N = int(input())
A = list(map(int, input().split()))
mod = 998244353

n = 2*10**5+5
fact = [1] * (n + 1)
invfact = [1] * (n + 1)
for i in range(1, n):
    fact[i + 1] = ((i+1) * fact[i]) % mod
invfact[n] = pow(fact[n], mod - 2, mod)
for i in range(n - 1, -1, -1):
    invfact[i] = invfact[i + 1] * (i + 1) % mod

def comb(n, r):
    if n < 0 or r < 0 or n - r < 0:
        return 0
    return fact[n] * invfact[r] * invfact[n - r] % mod

A.append(0)
now = A[0]
ans = 0
for i in range(1, N + 1):
    while now > A[i]:
        ans += comb(i - 1 + now, i - 1)
        ans %= mod
        now -= 1 
print((ans+1)%mod)