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;

class Program
{
    static void Main(string[] args) {
        double x = double.Parse(Console.ReadLine());
        Console.WriteLine(solve(x));
    }
    static double solve(double x) {
        double ans = 1;
        for(double i = 1; i < Math.Ceiling(Math.Sqrt(x)); i ++) {
            double j = 2;
            while(true) {
                double tmp = Math.Pow(i,j);
                if(tmp >= x) break;
                if(i == 1)break;
                if(ans < tmp) ans = tmp;
                j ++;
            }
        }
        return ans;
    }
}