import java.util.*;
public class Yain{
    static int fibo(int num)
    {
        if(num==1)
        return 0;
        if(num ==2)
        return 1;
        
        return (fibo(num-1)+fibo(num-2));
    }



    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        if(n<0)
        {
            System.out.print("Invalid input");
            return;
        }
        System.out.print(fibo(num));
    }
}