Problem:
Score : 200 points

Problem Statement

You are given a positive integer X.
Find the largest perfect power that is at most X.
Here, a perfect power is an integer that can be represented as b^p, where b is an integer not less than 1 and p is an integer not less than 2.

Constraints

1 ≤ X ≤ 1000

X is an integer.

Input

Input is given from Standard Input in the following format:

X

Output

Print the largest perfect power that is at most X.

Sample Input 1

10

Sample Output 1

9

There are four perfect powers that are at most 10: 1, 4, 8 and 9.
We should print the largest among them, 9.

Sample Input 2

1

Sample Output 2

1

Sample Input 3

999

Sample Output 3

961

Solution in PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
  
fscanf(STDIN,"%d",$x);
$count=0;

if($x==1){
  echo "1\n";
}else{
  for($i=$x;$i>1;$i--){
    $beki = $i;
	for($j=2;$j<$x;$j++){
      while($beki%$j==0){
        $beki /= $j;
        $count++;
        if($beki==1 && $count >= 2){ 
          echo $i."\n";
          exit;
        }
      }
              $count=0;

    }
  
  
  }
  
  
  
  
  
}