const MOD: usize = 998244353;

fn is_odd(n: usize, k: usize) -> bool {
    (n & k) == k
}

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut b = String::new();
    std::io::stdin().read_line(&mut b).ok();
    let b: Vec<isize> = b.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let mut dp = vec![0usize; n+1];
    let mut total = 1usize;
    for i in 0..n {
        let odd = is_odd(n-1, i);
        if b[i] == -1 {
            if odd {
                dp[i+1] = total;
            } else {
                dp[i+1] = 2*dp[i] % MOD;
            }
            total *= 2;
            total %= MOD;
        } else if b[i] == 1 && odd {
            dp[i+1] = MOD + total - dp[i];
            dp[i+1] %= MOD;
        } else {
            dp[i+1] = dp[i];
        }
    }
    println!("{}", dp[n]);
}