import java.util.*;
public class main{
    public static void main(String[] args) {
        try{
            int a;
            Scanner in=new Scanner(System.in);
            a=in.nextInt();
            
            in.close();
            System.out.print(f(a));
        }catch(Exception e){
            System.out.println("Input error!");
        }
    }
    public static int f(int n)
    {
    	if(n<=1) 
    		return n;
    	else
    		return f(n-1)+f(n-2);
    }
};