use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let mut dp: Vec<usize> = vec![0; n + 2];
    dp[0] = 1;
    for i in 0..n {
        dp[i + 1] += dp[i];
        dp[i + 2] += dp[i];
    }
    println!("{}", dp[n]);
}