Problem:
Score : 200 points

Problem Statement

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.

Sample Input 1

5

Sample Output 1

11

L_0=2

L_1=1

L_2=L_0+L_1=3

L_3=L_1+L_2=4

L_4=L_2+L_3=7

L_5=L_3+L_4=11

Thus, the 5-th Lucas number is 11.

Sample Input 2

86

Sample Output 2

939587134549734843

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
public class Main{
  public static void main(String[] args){
    try{
      BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
	  int N = Integer.parseInt(bf.readLine());
      long a = 2;
      long b = 1;
      long c = N == 0 ? a : N == 1 ? b : 0;
      for(int i = 2; i <= N; i++){
      	c = a+b;
        a = b;
        b = c;        
      }
      System.out.println(c);
    } catch(IOException e){}
  }
}