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) {
		Scanner scanner = new Scanner(System.in);

		int n = scanner.nextInt();
		long[] memo = { 2, 1 };
		long ans = 0;
		if (n >= 2) {
			for (int i = 0; i <= n - 2; i++) {
				ans = memo[0] + memo[1];
				memo[0] = memo[1];
				memo[1] = ans;
			}
		}else{
			if (n==1) {
				ans=1;
			}else {
				ans=2;
			}
		}

		System.out.println(ans);

		scanner.close();
	}

}