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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
    double numX;
    scanf("%lf", &numX);

    double outnum;

    for (double numA = 1; numA <= 31; numA++)
    {
        for (double pownum = 2; pownum <= 9; pownum++)
        {
            double ans = pow(numA, pownum);    
            if (ans <= numX)
            {
                outnum = ans;
            }
        }
    }

    printf("%d", (int)outnum);

    return 0;
}