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 (1.15.1) (judge verdict: Accepted)

use std::io;

fn main() {
    let mut s = String::new();
    io::stdin().read_line(&mut s).ok();
    let s: u32 = s.trim().parse().unwrap();

    let mut ans: u32 = 0;

    for x in 1..1001 {
        for y in 2..1001 {
            let x = x as u32;
            let y = y as u32;

            if x > s {
                break;
            }

            let z = x.pow(y) as u32;

            if z > s {
                break;
            }
            if z <= s && ans < z {
                ans = z;
            }
        }
    }
    println!("{}", ans);
}