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
//Request Question
function getq($get_word=null){
	if($get_word===null){
		return str_replace("\n","",fgets(STDIN));
	}else if($get_word===1){
		return explode(" ",str_replace("\n","",fgets(STDIN)));
	}
}

/*		START		*/
$X = getq();
if($X<=3){echo "1\n";exit;}
for ($i=$X; $i >= 1; $i--) { 
	for ($j=$X; $j >=2 ; $j--) { 
		if(pow($i,$j)<=$X){
			echo pow($i,$j)."\n";
			exit;
		}
	}
}
?>