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 Kotlin (1.0.0) (judge verdict: Accepted)

fun main(args: Array<String>) = println(run {
    val x = readLine()!!.toInt()

    val ok = BooleanArray(1001)
    ok[1] = true
    for (b in 2..31) {
        var k = b*b
        while (k<=1000) {
            ok[k] = true
            k *= b
        }
    }

    ok.take(x+1).withIndex().last { it.value }.index

})