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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func init() {
	sc.Split(bufio.ScanWords)
	sc.Buffer([]byte{}, math.MaxInt64)
}

func readFloat() float64 {
	sc.Scan()
	r, _ := strconv.ParseFloat(sc.Text(), math.MaxInt64)
	return r
}

func main() {
	x := readFloat()
	for i := x; i >= 1; i-- {
		sqrt := math.Sqrt(i)
		if sqrt == math.Floor(sqrt) {
			fmt.Println(i)
			break
		}
		cbrt := math.Cbrt(i)
		if cbrt == math.Floor(cbrt) {
			fmt.Println(i)
			break
		}
	}
}