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 {
        for j in 0..2 {
            if dp[i][j] == 0 { continue; }
            let odd = (n-1) & i == i;
            if b[i] == -1 {
                dp[i+1][j] += dp[i][j] + if !odd { dp[i][j] } else { 0 };
                dp[i+1][j^1] += if odd { dp[i][j] } else { 0 };
                dp[i+1][j] %= MOD;
                dp[i+1][j^1] %= MOD;
            } else {
                let val = if odd && b[i] == 1 { 1 } else { 0 };
                dp[i+1][j^val] += dp[i][j];
                dp[i+1][j^val] %= MOD;
            }
        }
    }
    println!("{}", dp[n][1]);
}