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.*;
public class Main{
public static void main(String[]args){
  Scanner sc=new Scanner(System.in);
  long a=2,b=1;
  int n=sc.nextInt();
  for(int i=0;i<n;i++){
  	long c=a;
    a=b;
    b+=c;
  }
  System.out.println(a);
}

}