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

    fscanf(STDIN,"%d",$N);
        $before1 = 2;
        $before_result = 1;
        // if($N==1){
        //     echo $before_result."\n";
        // }else{
            $l_now=0;
            for($i=1;$i<$N;$i++){
                $l_now = $before1+$before_result;
                $before1 = $before_result;
                $before_result = $l_now;
                echo "$l_now";
            }
        
            

            echo $l_now."\n";

        // }