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.*;
import java.math.BigInteger;
// warm-up
public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt()-1;
		BigInteger[] c = {new BigInteger("2"), BigInteger.ONE};
		while (N-->0) {
			BigInteger t = c[0].add(c[1]);
			c[0] = c[1];
			c[1] = t;
		}
		System.out.println(c[1]);
		sc.close();		
	}

	public static void main(String args[]) {
		solve();
	}

}