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 Java8 (OpenJDK 1.8.0) (judge verdict: Runtime Error)

import java.util.Scanner;
import java.util.TreeSet;

public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt();
		
		TreeSet<Integer> expo = new TreeSet<>();
		for(int i = 1; i < x; i++) {
			for(int n = 2; n < 10; n++) {
				double result = Math.pow((double)i,(double)n);
				if(result > x) {
					break;
				}else {
					expo.add((int)result);
				}
			}
		}
		
		System.out.println(expo.last());
	}
}