#![allow(non_snake_case)]

use std::io::{ self, prelude::* };

macro_rules! pick {
    ($tokens:expr) => {
        $tokens.next().unwrap().parse().expect("parse error")
    }
}

fn main() {
    let mut s = String::new();
    io::stdin().read_to_string(&mut s).expect("i/o error");
    let mut tokens = s.split_whitespace();

    let N: usize = pick!(tokens);

    let mut v = vec![0_u64; N+1];
    v[0] = 1;

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

    let ans = v[N];

    println!("{}", ans);
}