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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            var pri = new int[] { 2, 3, 5, 7, 11, 13, 17, 19, 23, 28, 31 };
            var X = int.Parse(Console.ReadLine());
            double ans = 1;

            foreach(var i in pri)
            {
                var count = 2;
                while (Math.Pow(i, count) <= X)
                {
                    if (Math.Pow(i, count) > ans) ans = Math.Pow(i, count);
                    count++;
                }
            }

            Console.WriteLine(ans);
        }
    }
}