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: Time Limit Exceeded)

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

int main(void){
    int X;
    scanf("%d", &X);
    int limit = (int)sqrt(X);
    int i, j;
    double ans = X;
    for(i=1; i<=limit; i++) {
        for(j=2; pow((double)i, (double)j) <= (double)X; j++) {
            if(pow((double)i, (double)j) > ans) {
                ans = pow((double)i, (double)j);
            }
        }
    }
    printf("%d\n", (int)ans);
    return 0;
}