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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define F first
#define S second
#define mkp(x, y) make_pair(x, y)

using namespace std;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef pair<int,int> pii;
ll a[22222];
int main()
{
	ll x;
	cin >> x;
	a[1] = 1;
	for(int i = 2; i <= 1000; i ++)
	{
		ll k = i*i;
		while(1)
		{
			if(k > 1000)
				break;
			a[k] = 1;
			k *= i;
		}
	}
	for(int i = x; i >= 1; i --)
	{
		if(a[i])
		{
			cout << i;
			return 0;
		}
	}
}