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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
  $N=fgets(STDIN);
  $L[0]=2;
  $L[1]=1;
  $cnt=2;

  if($N==1)
  {
    echo"$L[1]";
  }
  else
  {
    while($cnt<($N+1))
    {
      $L[$cnt]=$L[($cnt-1)]+$L[($cnt-2)];
      $cnt++;
    }
    echo"$L[$N]";
  }
?>