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)

fn main() {
    let s = getline();
    let list: Vec<_> = s.trim().split(' ').collect();

    let x: i32 = list[0].parse().unwrap();
    let y: f32 = x as f32;

    let z = y.sqrt().floor() as i32;

    let mut max: i32 = 1;

    for i in 2..(z + 1) {
        let mut tmp = 1;
        while tmp * i <= x {
            tmp *= i;
            if max < tmp {
                max = tmp;
            }
        }
    }
    println!("{}", max);
}


fn getline() -> String {
    let mut __ret = String::new();
    std::io::stdin().read_line(&mut __ret).ok();
    return __ret;
}