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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();

		long answer = 0;

		long l_num_befbef = -1;
		long l_num_bef    = 2;
		long now_num = 0;

		for(int i = 0; i < N; i++) {
			now_num = l_num_bef + l_num_befbef;
			l_num_befbef = l_num_bef;
			l_num_bef = now_num;

			answer = now_num;
		}

		System.out.println(answer);
	}

}