fn main() {
    let N: i64 = {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).unwrap();
        s.trim_right().to_owned().parse().unwrap()
    };
    println!("{}", num_pattern(N));
}

fn num_pattern(n: i64) -> i64 {
    if n == 1 {
        1
    } else if n == 2 {
        2
    } else if n == 3 {
        3
    } else {
        num_pattern(n-2)*2 + num_pattern(n-3)
    }
}