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 buff = String::new();
    std::io::stdin().read_to_string(&mut buff).unwrap();
    let mut iter = buff.split_whitespace();

    let x: i32 = iter.next().unwrap().parse().unwrap();
    let mut mx: i32 = 1;

    for i in 2..(x + 1) {
        let mut j: i32 = i * i;
        while j <= x {
            if mx <= j {
                mx = j;
            }
            j *= i;
        }
    }
    println!("{}", mx);
}