const MOD: usize = 998244353;

fn fact_inv(size: usize) -> (Vec<usize>, Vec<usize>) {
    let mut facts = vec![0usize; size+1];
    let mut fact_invs = vec![0usize; size+1];
    let mut invs = vec![0usize; size+1];
    facts[0] = 1;
    facts[1] = 1;
    fact_invs[0] = 1;
    fact_invs[1] = 1;
    invs[1] = 1;
    for i in 2..=size {
        facts[i] = facts[i-1] * i % MOD;
        invs[i] = MOD - invs[MOD % i] * (MOD / i) % MOD;
        fact_invs[i] = fact_invs[i - 1] * invs[i] % MOD;
    }
    (facts, fact_invs)
}

fn comb(n: usize, r: usize, facts: &Vec<usize>, fact_invs: &Vec<usize>) -> usize {
    facts[n] * fact_invs[r] % MOD * fact_invs[n-r] % MOD
}

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 (facts, fact_invs) = fact_inv(n);
    let mut dp = vec![vec![0usize; 2]; n+1];
    dp[0][0] = 1;
    for i in 0..n {
        let pattern = comb(n-1, i, &facts, &fact_invs) % 2;
        if b[i] == -1 {
            dp[i+1][0] = dp[i][0] + dp[i][pattern];
            dp[i+1][1] = dp[i][1] + dp[i][1-pattern];
            dp[i+1][0] %= MOD;
            dp[i+1][1] %= MOD;
        } else if b[i] == 0 {
            dp[i+1][0] = dp[i][0];
            dp[i+1][1] = dp[i][1];
        } else {
            dp[i+1][0] = dp[i][pattern];
            dp[i+1][1] = dp[i][1-pattern];
        }
    }
    println!("{}", dp[n][1]);
}