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 N = scanner.nextInt();
    System.out.println(luca(N));
  }

  private static long luca(int N) {
    N--;
    long a = 2;
    long b = 1;
    while (N > 0) {
      long c = a + b;
      a = b;
      b = c;
      N--;
    }
    return b;
  }
}