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::Read;


fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    let mut it = buf.split_whitespace();
    let x: i32 = it.next().unwrap().parse().unwrap();
    
    let mut ans = 1;
    for b in 2..x {
        let mut p = 2;
        loop {
            let tmp = b.pow(p);
            if tmp>x {
                break;
            }
            ans = std::cmp::max(ans, b.pow(p));
            p += 1;
        }
    }


    println!("{}", ans);
}