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 {

	public static void main(String[] args) {

		@SuppressWarnings("resource")
		Scanner num = new Scanner(System.in);
		int n = num.nextInt();
		long l0 = 2;
		long l1 = 1;
		long ln = 0;

		if(n==1)System.out.println(l1);
		else{
			for(int i=2; i<=n; i++) {
				ln=l1+l0;
				l0=l1;
				l1=ln;
			}
			System.out.println(ln);
		}
	}

}