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: Runtime Error)

import scala.io.StdIn
object Main extends App {
  // def calcPows(n:Int) = 
  val x = StdIn.readLine.toInt
  val r = math.sqrt(x).toInt
  val ans = (2 to r).map { i =>
    val e: Seq[Int] = for {
      j <- (2 to r)
      e = math.pow(i,j).toInt if(e <= x)
    } yield e
    e.max
  }
  println(ans.max)
}