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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.List

main = do
    x <- read <$> getLine
    print $ exponential x

exponential x = maximum [pow | b <- [1..x], let pow = maxPower b 2, pow <= x]
    where
        maxPower 1 p = 1
        maxPower b p =
            if (b^(p+1) <= x)
                then maxPower b (p + 1)
                else b^p