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: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml.Schema;
using static System.Console;

namespace ConsoleApp2
{
    class Program
    {
        static public int[] Sarray() { return ReadLine().Split().Select(int.Parse).ToArray(); }
        static public List<int> Slist() { return new List<int>(ReadLine().Split().Select(int.Parse)); }
        static void Main(string[] args)
        {
            var X = Sarray()[0];
            var expo = new bool[X + 1];
            expo[1] = true;
            for (var b = 2; b <= X; b++)
            {
                var v = b * b;
                while(v<=X)
                {
                    expo[v] = true;
                    v *= b;
                }
            }
            for(var i=X;i>=1;i--)
            {
                if(expo[i])
                {
                    WriteLine(i);
                    return;
                }
            }
        }
    }
}