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.io.File;
import java.io.IOException;
import java.util.*;
 
public class Main {
 
	public static void main(String[] args) throws IOException {
		//File file = new File("input.txt");
		//Scanner sc = new Scanner(file);
		
		Scanner sc = new Scanner(System.in);
		
		int N = sc.nextInt();
		if(N == 1) System.out.println(1);
		else{
			long n1 = 2, n2 = 1, n3 = 0;
			for(int i = 1; i < N; i++){
				n3 = n2 + n1;
				n1 = n2;
				n2 = n3;
			}
			System.out.println(n3);
		}
	}
}