//by Terram
package Trollololed;

import java.util.Scanner;

public class fibon {
	
	public static int fib(int x){	
		int d = 0;
		if(x==0){d=0;}
		if(x==1){d=1;}
		if(x>=2){d=fib(x-2) + fib(x-1);}
		return d;
	}

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int x = in.nextInt();
		System.out.print(fib(x));
	}
}