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 {
	static Scanner s = new Scanner(System.in);

	public static void main(String[] args) {

		int N = s.nextInt() + 1;
		long a = 2;
		long b = 1;
		long ans = 0;

		for (int i = 1; i < N - 1; i++) {
			ans = a + b;
			a = b;
			b = ans;
		}
		if (N == 2) {
			System.out.println(b);
		} else {
			System.out.println(ans);
		}
	}
}