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);
			int N = sc.nextInt();
			long[] lucas =new long[87] ;
			lucas[0]=2;lucas[1]=1;
			for(int i=2;i<=86;i++) 
				lucas[i]=lucas[i-2] + lucas[i-1];
			System.out.println(lucas[N]);
	}

}