use std::io::{stdin, BufRead};

fn main() {
    let stdin = stdin();
    let mut stdin = stdin.lock().lines().map(Result::unwrap);
    let n = stdin.next().unwrap().parse::<usize>().unwrap();
    let mut dp = [1_u64, 0];
    for _ in 0..n {
        dp = [dp[0] + dp[1], dp[0]];
    }
    let ans = dp[0];
    println!("{}", ans);
}