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 mut s=String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let mut n:usize=s.trim().parse().unwrap();
    let mut v=vec![false;n+1];
    v[1]=true;
    for i in 2..32{
        let mut x=i*i;
        while x<=n{
            v[x]=true;
            x*=i;
        }
    }
    while !v[n]{
        n-=1;
    }
    println!("{}",n);
}