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{
	public static void main(String[] args) {
		Scanner stdIn=new Scanner(System.in);
		int n=stdIn.nextInt(),i;
		long a[]=new long[3];
		a[0]=2;
		a[1]=1;
		for(i=0;i<n;i++) {
			a[2]=a[0]+a[1];
			a[0]=a[1];
			a[1]=a[2];
		}
		System.out.print(a[0]);
	}
}