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<bits/stdc++.h>
using namespace std;
int main(){
  int x;
  cin>>x;
  int a[50];
  set<int> s;
  for(int i=1;i<=31;i++){
    for(int j=2;j<=9;j++){
      int b=i;
      for(int k=0;k<j-1;k++) b*=b;
      if(1000<b) break;
      s.insert(b);
    }
  }
  auto itr = s.end();
  itr--;
    while (itr != s.begin()) {
        if(*itr<=x){ cout<<*itr; return 0; }
        itr--;
    }
}