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

fn main() {
    let input = io::stdin()
        .lock()
        .lines()
        .map(|l| {
            l.unwrap()
                .split_whitespace()
                .map(std::string::ToString::to_string)
                .collect::<Vec<_>>()
        })
        .collect::<Vec<_>>();

    let goal = input[0][0].parse::<u64>().unwrap();

    let mut f1 = 0u64;
    let mut f2 = 1u64;
    for _ in 0..goal {
        let tmp = f2;
        f2 += f1;
        f1 = tmp;
    }

    println!("{}", f2);
}