use std::io::*;
use std::str::FromStr;

#[allow(dead_code)]
fn get_line() -> String {
    let stdin = stdin();
    let mut line = String::new();
    stdin.lock().read_line(&mut line).expect("io error.");
    line.trim().to_string()
}

#[allow(dead_code)]
fn cast<T: FromStr>(s: &str) -> T {
    s.parse().ok().expect("parse error.")
}

#[allow(dead_code)]
fn get_vec<T: FromStr>() -> Vec<T> {
    (&get_line()).split(' ').map(cast::<T>).collect()
}


/* ---------- ここまでテンプレ ---------- */


fn main() {
    let n: usize = cast(&get_line());
    let mut dp: Vec<u64> = vec![0; n + 1];

    dp[0] = 1;
    for i in 0..n {
        if i + 1 <= n {dp[i + 1] += dp[i]};
        if i + 2 <= n {dp[i + 2] += dp[i]};
    }

    println!("{}", dp[n]);
}