const MOD: usize = 998244353;

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![vec![0usize; 2]; n+1];
    dp[0][0] = 1;
    for i in 0..n {
        let is_odd = (n-1) & i == i;
        let pat = if is_odd { 1 } else { 0 };
        match b[i] {
            -1 => { dp[i+1][0] = (dp[i][0] + dp[i][0^pat]) % MOD; dp[i+1][1] = (dp[i][1] + dp[i][1^pat]) % MOD; },
            0 => { dp[i+1][0] = dp[i][0]; dp[i+1][1] = dp[i][1]; },
            1 => { dp[i+1][0] = dp[i][0^pat]; dp[i+1][1] = dp[i][1^pat]; },
            _ => { unreachable!(); }
        }
    }
    println!("{}", dp[n][1]);
}