#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 10;
const int mod = 998244353;
int n, f[N];
int fac[N << 1];
int inv[N << 1];

// TODO
// 待复习完卡特兰数时，当做练习题来再次做这道题
// 2023-03-14
int qmi(int a, int b, int mod) {
    a %= mod;
    if (!a) return 0;
    int result = 1;
    for (; b; a = 1ll * a * a % mod, b >>= 1) {
        if (b & 1) result = 1ll * result * a % mod;
    }
    return result;
}

int C(const int n, const int m) {
    if (n < m) return 0;
    return 1ll * fac[n] * inv[m] % mod * inv[n - m] % mod;
}

int cal(int a, int b) {
    return (1ll * C(a + 2 * b, b) - C(a + 2 * b, b - 1) + mod) % mod;
}

void init(const int n) {
    fac[0] = 1;
    for (int i = 1; i <= n; i++) fac[i] = 1ll * fac[i - 1] * i % mod;
    inv[n] = qmi(fac[n], mod - 2, mod);
    for (int i = n - 1; i >= 0; i--) inv[i] = inv[i + 1] * (i + 1ll) % mod;
}
int main() {
    freopen("stack.in", "r", stdin);
    freopen("stack.out", "w", stdout);
    cin >> n;
    init(n << 1);
    for (int i = 1; i <= n; i++) cin >> f[i];
    int ans = 0;
    for (int i = 1; i <= n; i++)
        if (f[i]) ans = (ans + cal(i - 1, n - i)) % mod;

    cout << ans << endl;
    return 0;
}