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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		
		long[] memo = new long[n + 1];
		memo[0] = 2;
		memo[1] = 1;
		System.out.println(lucas(n, memo));
		
		sc.close();
	}
	
	static long lucas(int n, long[] memo) {
		if (memo[n] > 0) return memo[n];
		return memo[n] = lucas(n - 1, memo) + lucas(n - 2, memo);
	}
}