use std::io;
use std::io::prelude::*;

fn main() {
    let stdin = io::read_to_string(io::stdin()).unwrap();
    let mut stdin = stdin.split_ascii_whitespace();
    let stdout = io::stdout();
    let mut stdout = io::BufWriter::new(stdout.lock());

    let n: usize = stdin.next().unwrap().parse::<usize>().unwrap();

    let mut dp = vec![0u64; 51];
    dp[0] = 1;
    dp[1] = 1;
    for i in 2..=50 {
        dp[i] = dp[i - 1] + dp[i - 2];
    }

    writeln!(stdout, "{}", dp[n]);
}