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 whiteread::parse_line;

fn main() {
    let x: u32 = parse_line().unwrap();
    let mut ans: u32 = 1;

    for i in 2..=((x as f64).sqrt().floor()) as u32 {
        let mut k = 2;
        let exp = loop {
            if i.pow(k) > x {
                break k - 1;
            }
            k += 1;
        };
        ans = ans.max(i.pow(exp));
    }
    println!("{}", ans);
}