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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int x = in.nextInt();

        if(x == 1) {
            System.out.println(x);
        } else {
            for(int i = x; i >= 1; i--) {
                if(isPower(i)) {
                    System.out.println(i);
                    break;
                }
            }
        }

    }

    public static boolean isPower(int n) {
        if(n == 1) {
            return false;
        } else {
            for(int i = 2; Math.pow(n, 1.0/i) >= 2.0; i++) {
                double d = Math.pow(n, 1.0/i);
                if(d - Math.floor(d) == 0.0)
                    return true;
            }
        }

        return false;
    }
}