#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
using mint = modint998244353;
const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
// combination mod prime
// https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619
struct combination {
	std::vector<mint> fact, ifact;
	combination(int n) :fact(n + 1), ifact(n + 1) {
		assert(n < mod);
		fact[0] = 1;
		for (int i = 1; i <= n; ++i) fact[i] = fact[i - 1] * i;
		ifact[n] = fact[n].inv();
		for (int i = n; i >= 1; --i) ifact[i - 1] = ifact[i] * i;
	}
	mint operator()(int n, int k) { return com(n, k); }
	mint com(int n, int k) {
		//負の二項係数を考慮する場合にコメントアウトを外す
		//if (n < 0) return com(-n, k) * (k % 2 ? -1 : 1);
		if (k < 0 || k > n) return 0;
		return fact[n] * ifact[k] * ifact[n - k];
	}
	mint comsub(long long n, long long k) {
		if (n - k < k) k = n - k;
		assert(k < (int)fact.size());
		mint val = ifact[k];
		for (int i = 0; i < k; ++i) val *= n - i;
		return val;
	}
	template <typename ...Ms, std::enable_if_t<std::conjunction_v<std::is_integral<Ms>...>, std::nullptr_t> = nullptr>
	mint polynom(const int n, const Ms & ...ms) {
		mint res = fact[n];
		int sum = 0;
		for (int m : { ms... }) {
			if (m < 0 or m > n) return 0;
			res *= ifact[m];
			sum += m;
		}
		if (sum > n)return 0;
		res *= ifact[n - sum];
		return res;
	}
	mint div(int x) {
		if (x >= (int)fact.size())return mint(x).inv();
		return fact[x - 1] * ifact[x];
	}
	mint inv(int n, int k) {
		//if (n < 0) return inv(-n, k) * (k % 2 ? -1 : 1);
		if (k < 0 || k > n) return 0;
		return ifact[n] * fact[k] * fact[n - k];
	}
	mint p(int n, int k) { return fact[n] * ifact[n - k]; }
}c(2000006);
int f(const vector<int> &v) {
	int now = 0;
	int ret = 0;
	for (auto e : v) {
		if (0 == e)ret += now;
		else now++;
	}
	return ret;
}
// 01文字列(数列から単調増加列に変換する)
// 0:x++,1:y++
// ex:10100->[1,2,2]
std::vector<int> exchange01(const std::vector<int>&v) {
	int now = 0;
	std::vector<int>ret;
	for (auto e : v) {
		if (0 == e)ret.push_back(now);
		else now++;
	}
	return ret;
}
// 単調増加列に対して標準盤を数える
// O(n^2)
mint hookLengthFormula(const std::vector<int>&v) {
	if (v.empty())return 1;
	int sum = 0;
	for (auto e : v)sum += e;
	mint p = 1;
	for (int i = 1; i <= sum; ++i)p *= i;

	mint q = 1;
	std::vector<int>cnt(v.back() + 1);
	for (int i = 0; i < (int)v.size(); ++i) {
		for (int j = 1; j <= v[i]; ++j) {
			int tmp = cnt[j] + v[i] - j + 1;
			q *= tmp;
			cnt[j]++;
		}
	}
	return p * q.inv();
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<int>a(n);
	rep(i, n)cin >> a[i];
	int sum = 0;
	rep(i, n)sum += a[i];
	vector<int>str01;
	rep(i, n) {
		int x = 0 == i ? a[i] : a[i] - a[i - 1];
		rep(j, x)str01.push_back(1);
		str01.push_back(0);
	}

	vector<int>str01A, str01B;
	rep(i, str01.size()) {
		if (i % 2 == 0)str01A.push_back(str01[i]);
		else str01B.push_back(str01[i]);
	}
	int sumA = f(str01A), sumB = f(str01B);
	if ((sumA + sumB) * 2 != sum) {
		cout << 0 << endl;
		return 0;
	}
	mint ans = c(sumA + sumB, sumA);
	ans *= hookLengthFormula(exchange01(str01A));
	ans *= hookLengthFormula(exchange01(str01B));
	cout << ans.val() << endl;
	return 0;
}