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: Wrong Answer)

use std::io;

fn read_line() -> String {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    s
}

macro_rules! from_line {
    ($($a:ident : $t:ty),+) => {
        $(let $a: $t;)+
        {
            let _line = read_line();
            let mut _it = _line.trim().split_whitespace();
            $($a = _it.next().unwrap().parse().unwrap();)+
                assert!(_it.next().is_none());
        }
    };
}

fn issquare(n: u64, p: u64) -> bool {
    if ((n as f64).powf(1.0/(p as f64)) as u64).pow(p as u32) == n {
        true
    }
    else {
        false
    }
}

fn main() {
    from_line!(x: u64);
    let mut ret = false;
    for i in (1..x+1).rev() {
        if ret {
            break;
        }
        for j in 2..10 {
            if issquare(i, j) {
                println!("{}", i);
                ret = true;
                break;
            }
        }
    }
}