#[allow(unused)]
use proconio::{input, marker::Chars};

fn main() {
    input! {
        n: usize,
    }
    let mut dp = vec![0usize; n + 1];
    dp[0] = 1;
    dp[1] = 1;
    for i in 2..=n {
        dp[i] += dp[i - 1] + dp[i - 2];
    }
    println!("{}", dp[n])
}