fn read<T: std::str::FromStr>() -> T {
  let mut s = String::new();
  std::io::stdin().read_line(&mut s).ok();
  s.trim().parse().ok().unwrap()
}

fn main() {
  let n: i64 = read();
  println!("{}", no44(n));
}

fn no44(n: i64) -> i64 {
  use std::collections::HashMap;
  let mut cache = HashMap::new();
  
  fn consumer(n: i64, cache: &mut HashMap<i64, i64>) -> i64 {
    if let Some(ans) = cache.get(&n) {
      return *ans;
    }
    if n - 2 > 0 {
      let ans = consumer(n - 1, cache) + consumer(n - 2, cache);
      cache.entry(n).or_insert(ans);
      ans
    } else if n - 2 == 0 {
      2
    } else if n - 1 == 0 {
      1
    } else {
      0
    }
  }
  consumer(n, &mut cache)
}