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: Accepted)

use proconio::{fastout, input};

#[fastout]
fn main() {
    input!(x: usize);
    if x == 1 {
        println!("1");
        return;
    }

    let mut b_v = vec![false; 1001];

    for v in 1..x {
        for i in 2..1000f32.sqrt() as u32 {
            let buff = v.pow(i) as usize;
            if buff > 1000 {
                break;
            }
            b_v[buff] = true;
        }
    }

    for i in (0..x + 1).rev() {
        if b_v[i] {
            println!("{}", i);
            return;
        }
    }
}