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.Arrays;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner in = new java.util.Scanner(System.in);
		//String N = in.nextLine();
		int N = in.nextInt();
		long L0 = 2;
		long L1 = 1;
		if(N==1) {
			System.out.println(L1);
			System.exit(0);
		}
		int i=1;
		long L=1;
		while(i<N) {
			L = L1 + L0;
			L0 = L1;
			L1 = L;
			i++;
		}
		System.out.println(L);
		
		
		in.close();
	}
}