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