fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();

    let mut dp = vec![0usize; n+1];
    dp[0] = 1;
    for i in 0..n {
        dp[i+1] += dp[i];
        if i+2 <= n {
            dp[i+2] += dp[i];
        }
    }
    println!("{}", dp[n]);
}