#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define ar array
#define vt vector
#define pq priority_queue
#define pu push
#define pub push_back
#define em emplace
#define emb emplace_back
#define mt make_tuple

#define all(x) x.begin(), x.end()
#define allr(x) x.rbegin(), x.rend()
#define allp(x, l, r) x.begin() + l, x.begin() + r
#define len(x) (int)x.size()
#define uniq(x) unique(all(x)), x.end()

using ll = long long;
using ld = long double;
using ull = unsigned long long;

template <class T, size_t N>
void re(array <T, N>& x);
template <class T> 
void re(vt <T>& x);

template <class T> 
void re(T& x) {
    cin >> x;
}

template <class T, class... M> 
void re(T& x, M&... args) {
    re(x), re(args...);
}

template <class T> 
void re(vt <T>& x) {
    for(auto& it : x) re(it);
}

template <class T, size_t N>
void re(array <T, N>& x) {
    for(auto& it : x) re(it);
}

template <class T, size_t N>
void wr(const array <T, N>& x);
template <class T> 
void wr(const vt <T>& x);

template <class T> 
void wr(const T& x) {
    cout << x;
}

template <class T, class ...M>  
void wr(const T& x, const M&... args) {
    wr(x), wr(args...);
}

template <class T> 
void wr(const vt <T>& x) {
    for(auto it : x) wr(it, ' ');
}

template <class T, size_t N>
void wr(const array <T, N>& x) {
    for(auto it : x) wr(it, ' ');
}

template<class T, class... M>
auto mvt(size_t n, M&&... args) {
    if constexpr(sizeof...(args) == 1)
        return vector<T>(n, args...);
    else
        return vector(n, mvt<T>(args...));
}

void set_fixed(int p = 0) {
    cout << fixed << setprecision(p);
}

void set_scientific() {
    cout << scientific;
}

void Open(const string& name) {
#ifndef ONLINE_JUDGE
    (void)!freopen((name + ".in").c_str(), "r", stdin);
    (void)!freopen((name + ".out").c_str(), "w", stdout);
#endif
}

const int mod = 998'244'353;

template <unsigned MOD> struct modint {
    using M = modint;

    unsigned x;
    modint(ll x = 0) { fix(x % MOD + MOD); }

    inline M& fix(unsigned _x) {
        x = (_x < MOD)? _x : _x - MOD;
        return *this;
    }

    explicit operator bool() const { return x != 0; }
    explicit operator long long() const { return x; } 
    
    inline bool operator == (const M& other) const { return x == other.x; }
    inline bool operator != (const M& other) const { return x != other.x; }
    inline bool operator <  (const M& other) const { return x <  other.x; }
    inline bool operator >  (const M& other) const { return x >  other.x; }
    inline bool operator <= (const M& other) const { return x <= other.x; }
    inline bool operator >= (const M& other) const { return x >= other.x; }

    inline M operator  + () const { return M().fix(x); }
    inline M operator  - () const { return M().fix(MOD - x); }
    inline M& operator ++ ()       { this-> fix(x + 1); return *this; } 
    inline M  operator ++ (int)    { M tmp(*this); ++(*this); return tmp; }
    inline M& operator -- ()       { this-> fix(x - 1 + MOD); return *this; }
    inline M  operator -- (int)    { M tmp(*this); --(*this); return tmp; }

    inline M operator + (const M& other) const { return M().fix(x + other.x); }
    inline M operator - (const M& other) const { return M().fix(x + MOD - other.x); }     
    inline M operator * (const M& other) const { return M().fix((ull)x * other.x % MOD); } 
    inline M operator / (const M& other) const { return *this * other.inv(); }

    inline M& operator += (const M& other) { return *this = *this + other; }
    inline M& operator -= (const M& other) { return *this = *this - other; }
    inline M& operator *= (const M& other) { return *this = *this * other; } 
    inline M& operator /= (const M& other) { return *this = *this / other; } 

    M lgput(ll b) const {
        M a = *this, res = 1; 
        while (b) {
            if (b & 1) res *= a; 
            a *= a;
            b >>= 1;
        }
        return res;
    }

    M inv() const { return lgput(MOD - 2); }

    friend M operator + (const ll&  value, const M& n) { return n + M(value); }
    friend M operator + (const int& value, const M& n) { return n + M(value); }
    friend M operator - (const ll&  value, const M& n) { return n - M(value); }
    friend M operator - (const int& value, const M& n) { return n - M(value); }
    friend M operator * (const ll&  value, const M& n) { return n * M(value); }
    friend M operator * (const int& value, const M& n) { return n * M(value); }

    friend istream& operator >> (istream& in, M& n) { ll x; in >> x; n = x; return in; }
    friend ostream& operator << (ostream& os, const M& n) { return os << n.x; }
};

using mint = modint<mod>;

const int N = 1e6 + 1;
mint fact[N], ifact[N];

void prec() {
    fact[0] = ifact[0] = 1;
    fact[1] = ifact[1] = 1;
    for (int i = 2; i < N; ++i)
        fact[i] = fact[i - 1] * i;

    ifact[N - 1] = fact[N - 1].inv();
    for (int i = N - 2; i >= 2; --i)
        ifact[i] = ifact[i + 1] * (i + 1);
}

mint nCr(int n, int k) {
    if (n < 0 || k < 0 || k > n) return 0;
    return fact[n] * ifact[k] * ifact[n - k];
}

mint hookLength(vt <int> hook) {
    if (hook.empty()) return mint(1);
 
    sort(all(hook));
    std::vt <int> hook_t(hook.back());
 
    int sum = 0;
    mint num(1), den(1);
    for (int l : hook) {
        for (int j = 0; j < l; ++j) {
            num *= ++sum;
            den *= (++hook_t.at(j)) + l - 1 - j;
        }
    }
    return num / den;
}

void solve() {
    int n; re(n);
    vt <int> a(n); re(a);
    a.insert(a.begin(), 0);

    string s;
    for (int i = 1; i <= n; ++i)
        s += string(a[i] - a[i - 1], '1') + '0';

    int s0 = 0, s1 = 0; 
    vt <int> even, odd;
    for (int i = 0, cnt = 0; i < len(s); i += 2)
        if (s[i] == '0') s0 += cnt, even.pub(cnt);
        else ++cnt;

    for (int i = 1, cnt = 0; i < len(s); i += 2)
        if (s[i] == '0') s1 += cnt, odd.pub(cnt);
        else ++cnt;

    if (2 * (s0 + s1) != accumulate(all(a), 0))
        return wr("0\n");

    mint res = 1;
    res = nCr(s0 + s1, s0) * hookLength(even) * hookLength(odd);
    wr(res);
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    //Open("");

    prec();

    int t = 1;
    for(;t;t--) {
        solve();
    }
    
    return 0;
}