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::*;
use std::str::FromStr;

fn main(){
    let x = read::<u32>();
    if x==1{
        println!("{}", 1);
    }else{
        let mut max = 1;
        for i in 2..x{
            let mut j : u32 = 2;
            let mut m = 0;
            while true{
                let p = i.pow(j);
                if p > x{
                    break;
                }else{
                    m = p;
                    j += 1;
                }
            }
            if m > max{
                max = m;
            }
        }
        println!("{}", max);
    }
}
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin.bytes().map(|c| c.expect("Error") as char) 
        .skip_while(|c| c.is_whitespace()).take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("Error")
}