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 JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

'use strict';

function Main(input) {
  const X = Number(input);
  let list = [];

  for(let i=1; i<32; i++) {
    for(let j=2; j<11; j++) {
      if(Math.pow(i,j) < 1000) {
        list.push(Math.pow(i,j))
      }
    }
  }
  list.sort(function(a,b) {return a<b ? 1:-1;});  
  
  let listleng = list.length;

  for(let k=0; k<listleng; k++) {
    if(list[k] <= X) {
      console.log(list[k]);
      break;
    }
  }
  
}
 
Main(require("fs").readFileSync("/dev/stdin", "utf8"));