fn main() {
	let mut n = String::new();
	std::io::stdin().read_line(&mut n).ok();
	let n: usize = n.trim().parse().unwrap();
	
	let mut d: Vec<usize> = vec![0; n + 2];
	d[0] = 1;

	for i in 0..n {
		d[i + 1] += d[i];
		d[i + 2] += d[i];
	}
	
	println!("{}", d[n]);
}