def nPr(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    return g1[n] * g2[n-r] % mod

def nCr(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return (g1[n] * g2[r] % mod) * g2[n-r] % mod

import sys
input = sys.stdin.readline
MOD = 998244353
N = int(input())
A = list(map(int, input().split()))

g1 = [1, 1] # 元テーブル
g2 = [1, 1] #逆元テーブル
inverse = [0, 1] #逆元テーブル計算用テーブル
fact = [1, 1]

for i in range( 2, 2*10**5 + 1 ):
    g1.append( ( g1[-1] * i ) % MOD )
    inverse.append( ( -inverse[MOD % i] * (MOD//i) ) % MOD )
    g2.append( (g2[-1] * inverse[-1]) % MOD )
    fact.append( (fact[-1] * i) % MOD )

A.append(0)
ans = dict()
for i in range(N):
    a = A[i]
    ans[(i, a)] = nCr(i+a, a, MOD)
    a2 = A[i+1]
    for aa in range(a2, a):
        ans[(i+1, aa)] = nCr(i+1+aa, aa, MOD)
#print(ans)
ans2 = 0       
for key in ans:
    i, a = key
    ans2 += ans[key]
    ans2 %= MOD
    if (i-1, a) in ans:
        ans2 -= ans[(i-1, a)]
        ans2 %= MOD
    if (i, a-1) in ans:
        ans2 -= ans[(i, a-1)]
        ans2 %= MOD
print(ans2)