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.io.*;
public class Main{
  public static void main(String[] args){
    try{
      BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
	  int N = Integer.parseInt(bf.readLine());
      long a = 2;
      long b = 1;
      long c = N == 0 ? a : N == 1 ? b : 0;
      for(int i = 2; i <= N; i++){
      	c = a+b;
        a = b;
        b = c;        
      }
      System.out.println(c);
    } catch(IOException e){}
  }
}