MOD = 998244353

def HookLengthFormula(A, MOD=998244353):
    n = len(A)
    if n == 0:
        return 1
    tot = sum(A)
    ans = 1
    for i in range(1, tot + 1):
        ans *= i
        ans %= MOD
    
    inv = 1
    r = n - 1
    for i in range(A[0]):
        while A[r] == i:
            r -= 1
        for j in range(r, -1, -1):
            h = r - j + A[j] - i
            inv *= h
            inv %= MOD
    ans = ans * pow(inv, MOD - 2, MOD) % MOD
    return ans

n = int(input())
A = list(map(int, input().split()))
tot = sum(A)
if tot & 1:
    print(0)
    exit()

binary = []
b = 0
for a in A:
    binary += [0] * (a - b) + [1]
    b = a

P = binary[0::2]
Q = binary[1::2]

op = P.count(1)
oq = Q.count(1)
if op == oq:
    pass
elif len(P) == len(Q) and op + 1 == oq:
    pass
elif op == oq + 1:
    pass
else:
    print(0)
    exit()

def f(P):
    A = []
    x = 0
    for p in P:
        if p == 0:
            x += 1
        else:
            A.append(x)

    A = A[::-1]
    
    return HookLengthFormula(A), sum(A)

def nCk(n, k):
    ret = 1
    for i in range(n, n - k, -1):
        ret *= i
        ret %= MOD
    inv = 1
    for i in range(1, k + 1):
        inv *= i
        inv %= MOD
    return ret * pow(inv, MOD - 2, MOD) % MOD

pp, lp = f(P)
qq, lq  = f(Q)
ans = (pp * qq % MOD) * nCk(lp + lq, lp) % MOD
print(ans)