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 pattern = if (n-1)&i == i { 1 } else { 0 };
        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]);
}