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 <math.h>


int main(void)
{
    int X, ans;
    int i;
    scanf("%d", &X);
    ans=1;
    if(X == 1) {
        ans = 1;
    }else {
        i = 2;
        while (pow((double)X,1.0/(double)i)-2.0>-1e-20) {
            if(pow((int)(pow((double)X,1.0/(double)i)),i) > ans) {
                ans = pow((int)(pow((double)X,1.0/(double)i)), i);        
            }
            i++;
        }
    }
    printf("%d\n", ans);
    return 0;
}