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 Scala (2.11.7) (judge verdict: Accepted)

import scala.io.{StdIn => in}

object Main extends App {
  val x = in.readInt
  def rec(acc:Int, b:Int, p:Int):Int = {
    if(b == 1) return acc
    val res = math.pow(b,p).toInt
    // println(res)
    if(res > x) acc
    else rec(res, b, p+1)
  }
  val ans = (1 to math.sqrt(x).toInt + 1)./:(1)( (acc, i) => {
    val y = rec(i, i, 2)
    if(y <= x) acc max y else acc
  })
  println(ans)
}