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 scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        int i1,i2;
        long l1 = 1;
        long l2 = 1;
        for (int k = 0;k < i - 2;++k){
            long l3 = l1;
            l1 = l2;
            l2 += l3;
        }
        if(i == 1){
            l1 = 0;
        }
        System.out.println(l1 * 2 + l2);
    }


}