#include <bits/stdc++.h>
using namespace std;

int main() {
    constexpr int64_t mod = 998244353;
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    vector<vector<int64_t>> dp(n + 1, vector<int64_t>(5)); // dp[i][j] = i-th, j - 2
    int64_t ans = 0, d = 1, r = 1;
    for (int i = 0; i < n; i++) {
        dp[i][3] += d;
        for (int j = 0; j <= 4; j++) {
            int j_next = 2 + (j - 2) * a[i];
            if (0 <= j_next and j_next <= 4) {
                dp[i + 1][j_next] += dp[i][j];
                dp[i + 1][j_next] %= mod;
            }
        }
        if (i) d *= 2;
        d %= mod;
        ans *= 2;
        ans += dp[i + 1][0];
        ans %= mod;
        r *= (mod + 1) / 2;
        r %= mod;
    }
    ans += dp[n][0];
    ans %= mod;

    cout << ans * r % mod << endl;
}