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) {
		Scanner sc = new Scanner(System.in);
long n0=2;
long n1=1;
long n2=3;
int n=sc.nextInt();
if(n==0){
	System.out.println(2);
}else if(n==1){
	System.out.println(1);
}else{
for(int i=2;i<=n;i++){

	n2=n0+n1;
	n0=n1;
	n1=n2;

	}
System.out.println(n2);

	}}}