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:
//package reedeka;
import java.util.*;
import java.math.*;
public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int n;
		n = sc.nextInt();
		//System.close();
		long t1 = 2, t2 = 1;
		int i;
		long s = t2;
		if(n==0) {
			s = t1;
		}
		else {
		for(i=2; i<=n; i++) {
			s = t1 + t2;
			t1 = t2;
			t2 = s;
		}
		}
		System.out.println(s);
	}
}