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.math.BigDecimal;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		BigDecimal L0 = new BigDecimal(2);
		BigDecimal L1 = new BigDecimal(1);
		BigDecimal result = new BigDecimal(0);
		if (N == 1) {
			result = new BigDecimal(1);
		} else {
			for (int i = 2; i <= N; i++) {
				result = L0.add(L1);
				L0 = L1;
				L1 = result;
			}
		}
		System.out.println(result);
	}
}