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 {
	static int N;
	static long ans;
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	N=sc.nextInt();
    	luca(2,1,0);
    	System.out.println(ans);

	}
	public static void luca(long a,long b,int n) {
		if(n>=N) {
			ans=a;
			return;
		}
		luca(b,a+b,n+1);
	}
}