Problem: It is November 18 now in Japan. By the way, 11 and 18 are adjacent Lucas numbers.

You are given an integer N. Find the N-th Lucas number.

Here, the i-th Lucas number L_i is defined as follows:

* L_0=2
* L_1=1
* L_i=L_{i-1}+L_{i-2} (i≥2)

Constraints

* 1≤N≤86
* It is guaranteed that the answer is less than 10^{18}.
* N is an integer.

Input

Input is given from Standard Input in the following format:


N


Output

Print the N-th Lucas number.

Examples

Input

5


Output

11


Input

86


Output

939587134549734843

Solution (in JAVA):

Solution:
import java.util.Scanner;
public class Main{
    public static void main(String args[]){
        Scanner scan=new Scanner(System.in);
        int N=scan.nextInt();
        long[] L=new long[3];
        int i;
        L[0]=2;
        L[1]=1;
        for(i=2;i<=N;i++){
            L[i%3]=L[(i+1)%3]+L[(i+2)%3];
            //System.out.println(L[i%3]);
        }
        System.out.println(L[(i-1)%3]);
    }
}