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{
	static long Lucas(int k){
		long Li = 2;
		long Lj = 1;
		long Lk = 0;
		if(k==1)return 1;
		if(k==2)return 3;
		for(int i=0; i<k-1; i++){
			Lk = Lj + Li;
			Li = Lj;
			Lj = Lk;
		}
		return Lk;
	}

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		System.out.println(Lucas(n));
	}
}