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:usize = read();
    let mut dp = [0usize; 51];
    dp[0] = 1usize;
    dp[1] = 1usize;

    for i in 2..51 {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    println!("{:?}", dp[n]);
}