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 <math.h>
#include <stdio.h>

int ispower(int n) {
	int a, b;

	for (a = 1; a < 15; a++)
		for (b = 2; b < 15; b++)
			if (pow(a, b) == n)
				return 1;
	return 0;
}

int main() {
	int x, n, max;

	scanf("%d", &x);
	max = 0;
	for (n = 1; n <= x; n++)
		if (ispower(n) && max < n)
			max = n;
	printf("%d\n", max);
	return 0;
}