from sys import stdin
def input(): return stdin.readline()[:-1]

MOD = 998244353

MAXN = (10 ** 5 * 2) + 23
fact = [1] * MAXN
for i in range(1, MAXN):
    fact[i] = fact[i - 1] * i % MOD
inverse = [1] * MAXN
inverse[MAXN - 1] = pow(fact[MAXN - 1], MOD - 2, MOD)
for i in range(MAXN - 2, 0, -1):
    inverse[i] = inverse[i + 1] * (i + 1) % MOD

def comb(n, k):
    ans = fact[n] * inverse[k] % MOD
    ans = ans * inverse[n - k] % MOD
    return ans

def func(x, y):
    r, l = x - 1, y - 1
    return comb(r + l, r)
    

def solve():
    n = int(input())
    arr = list(map(int, input().split()))
    arr.append(0)
    
    t = [(1, arr[0] + 1)]
    for i in range(1, n + 1 ):
        if arr[i] == arr[i - 1]:
            row = i + 1
            right = arr[i] + 1 - 1
            t.append((row, right))
        else:
            row = i + 1
            right = arr[i] + 1
            t.append((row, right))
            right += 1
            while right <= arr[i - 1]:
                nrow = row - 1
                t.append((nrow, right))
                right += 1
    
    
    ans = 0
    for x, y in t:
        # print(x, y , func(x, y))
        ans += func(x, y)
        ans %= MOD
    print(ans)
    
    
solve()