// editor3
import java.util.*;
public class main{
    static int fib(int n){
        if(n<=1){
            return 0;
        }
        if(n==2)
        {
        return 1;
        }
        int term1 = fib(n-1);
        int term2 = fib(n-2);
        return term1+term2;
    }
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
       if(n<0){
           System.out.println("Invalid input");
           return ;
       }
       System.out.println(fib(r));
    }
}