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;
class Main{
	static Scanner s=new Scanner(System.in);
	static int gInt(){return Integer.parseInt(s.next());}
	public static void main(String[]$){
		long[]l=new long[87];
		l[0]=2;
		l[1]=1;
		for(int i=2;i<87;++i)
			l[i]=l[i-1]+l[i-2];
		System.out.println(l[gInt()]);
	}
}