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.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		//String S = sc.next();
		//int N = sc.nextInt();
		//System.out.println();
		int N = sc.nextInt();
		long a1 = 2;
		long a2 = 1;
		long lucas = 3;
		if(N==1){
			System.out.println(a2);
		}else{
			for(int i=1; i<N;i++){
				lucas = a1 + a2;
				a1 = a2;
				a2 = lucas;
			}
			System.out.println(lucas);
		}
			
	}
}