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 Rust (1.42.0) (judge verdict: Runtime Error)

#![allow(unused_macros)]
#![allow(dead_code)]
#![allow(unused_imports)]

use text_io::*;
use itertools::Itertools;
use std::collections::HashSet;

const U_INF: usize = 1 << 60;
const I_INF: isize = 1 << 60;

fn main(){
    let x : usize = read!();
    let mut v =HashSet::new() ;

    for i in 2..=x{
        let mut j = 2;
        while x>=i.pow(j) {
            v.insert(i.pow(j));
            j+=1;
        }
    }

    println!("{}", v.iter().max().unwrap());
}