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;

namespace B.Exponential
{
    class Program
    {
        static void Main(string[] args)
        {
            var X = int.Parse(Console.ReadLine());
            int ans = 0;

            for (int b = 1; b <= Math.Floor(Math.Sqrt(X)); b++)
            {
                for (int p = 2; Math.Pow(b, p) <= X; p++)
                {
                    ans = Math.Max(ans, (int)Math.Pow(b,p));
                    if (b == 1) break;
                }
            }
            Console.WriteLine(ans);
        }
    }
}