use std::io;

fn main() {
    let mut input = String::new();
    io::stdin().read_line(&mut input).unwrap_or(0);
    let n = input.trim().parse::<i32>().unwrap_or(0);
    println!("{}", fibonacci(n));
}

fn fibonacci(n: i32) -> i32 {
    let mut a = 0;
    let mut b = 1;
    for _ in 0..n {
        let temp = a;
        a = b;
        b = temp + b;
    }
    a
}