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 Ruby (2.3.3) (judge verdict: Accepted)

x = gets.to_i
arr = [1000, 961, 900, 841, 784, 729, 676, 625, 576, 529, 512, 484, 441, 400, 361, 343, 324, 289, 256, 243, 225, 216, 196, 169, 144, 128, 125, 121, 100, 81, 64, 49, 36, 32, 27, 25, 16, 9, 8, 4, 1]
puts arr.find{|item| item <= x}