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: Wrong Answer)

#include <iostream>
using namespace std;
int check(int a)
{
    int i=2, f=0, tmp;
    tmp=a;
    while(tmp>1){
        if(tmp%i==0){
          tmp=tmp/i;
          f=1;  
        } 
        else{
            i++;
            if(f==1) return  -1;
        }
    }
    if(i==a) return -1;
    return a;
}
int main()
{
    int x, ans;
    cin >>x;

    while(1){
        ans=check(x);
        if(ans>=0) break;
        x--;
    }
    cout << ans <<endl;
    return 0;
}