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 "time.h"
#include "unistd.h"
#include "string.h"
#include <math.h>
int ans=0;
int main(int argc, char* argv[]){
  long int a=0,b=0,c=0,e[5];
  float d=0;
  scanf("%f",&d);
  for (float i = d;; i--) {
    for (float j = 2; j < 10; j++) {
      float g=powf(i,1.0/j);
      if (fmodf(g,1.0)==0) {
        printf("%.0f",i);
        return 0;
      }
    }
  }
}