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 <stdlib.h>
#include <math.h>
#include <stdbool.h>
#define PI 3.141592653589793238462643383279

int x;
int num[] = {1,4,8,9,16,25,27,32,36,49,64,81,100,121,125,128,144,169,196,216,225,243,256,289,324,343,361,400,441,484,512,529,576,625,676,729,784,841,900,961,1000};

void change(int *x, int *y){
	int z;
	z = *x;
	*x = *y;
	*y = z;
}
int compare_int(const void *a, const void *b){
	return *(int*)a - *(int*)b;
}

int main(void){
	scanf("%d", &x);
	if(x==1000)	printf("1000");
  	else{
      for(int i=0;;i++){
		if(num[i]<=x && x<num[i+1]){
          printf("%d", num[i]);
          break;
      	  }
		}
    }
	return 0;
}