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.BigInteger;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner((System.in));
		int N = sc.nextInt();
		BigInteger a = BigInteger.ZERO, b = BigInteger.ZERO, c = BigInteger.ZERO;

		a = BigInteger.valueOf(2);
		b = BigInteger.ONE;
		c = BigInteger.ONE;

		for (int i = 1; i < N; i++) {
			c = a.add(b);
			a = b;
			b = c;
		}

		System.out.println(c);

		sc.close();
	}
}