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;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text.RegularExpressions;
using Console = System.Console;

namespace Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var X = int.Parse(Console.ReadLine());
            if (X == 1)
            {
                Console.WriteLine(1);
            }

            double ret = 0;
            for (int i = 2; i < X; i++)
            {
                for (int j = 2; j < 1000; j++)
                {
                    var cal = Math.Pow(i, j);
                    if (cal > X)
                    {
                        break;
                    }
                    if (ret < cal)
                    {
                        ret = cal;
                    }
                }
            }
            Console.WriteLine(ret);
        }
    }
}