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: Accepted)

#include <stdio.h>
#include <math.h>
int main(){
  int x;
  int ans=0;
  scanf("%d",&x);
  for(int i=0;i<x;i++){
    int judge_num = x-i; //判定する数を1ずつ小さくしていく
    for(int j=2;j<10;j++){
      if((int)pow(ceil(pow(judge_num,(double)1/j)),j)==judge_num){ 
        //n乗根の整数部分をn乗してjudge_numに戻ればそれはべき乗数
        printf("%d",judge_num);
        return 0;
      }
    }
  }
}