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 C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Linq;
namespace Sample
{
  class Sample
  {
    static void Main(string[] args)
    {
    int N=int.Parse(Console.ReadLine());
    long[] Lucas=new long[N+1];
      Lucas[0]=2;
      Lucas[1]=1;
      for(int i=2;i<=N;i++){
        Lucas[i]=Lucas[i-1]+Lucas[i-2];
      }
      Console.WriteLine(Lucas[N]);
    }
    
  }

}