package StackAndQueue;
import java.util.*;
public class RecursiveFibonacci {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        ArrayDeque<Long> Fibonacci = new ArrayDeque<>();
        long N = Integer.parseInt(input.nextLine());
            System.out.println(getFibonacci(Fibonacci, N));
    }

    private static Long getFibonacci(ArrayDeque<Long> Fibonacci, Long N) {
        if(N ==1 || N == 2){
            return 1L;
        }else {
            Fibonacci.offer(0L);
            Fibonacci.offer(1L);
            for (int i = 0; i < N; i++) {
                long Sum = Fibonacci.poll()+Fibonacci.peek();
                Fibonacci.offer(Sum);
            }
        }
        Fibonacci.poll();
        return Fibonacci.peek();
    }
}