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: Accepted)

package main

import (
	"bufio"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"strconv"
	"strings"
)

func (p *problem) solve() {
	X := p.NextInt()

	if X == 1 {
		p.PrintInt(1)
		return
	}

	ans := 1
	for p := 2; ; p++ {
		v := p * p
		if v > X {
			break
		}
		for v <= X {
			ans = max(v, ans)
			v *= p
		}
	}
	p.PrintInt(ans)
}

func max(x, y int) int {
	if x > y {
		return x
	}
	return y
}

var (
	debug  bool
	output string
)

func main() {
	flag.BoolVar(&debug, "debug", false, "Print debug logs")
	flag.BoolVar(&debug, "d", false, "Print debug logs")
	flag.StringVar(&output, "output", "stdout", "Specify output target (Default: stdout)")
	flag.StringVar(&output, "o", "stdout", "Specify output target (Default: stdout)")
	flag.Parse()

	if debug {
		out := os.Stdout
		if output != "stdout" {
			logfile, err := os.OpenFile(output, os.O_CREATE|os.O_WRONLY, 0666)
			if err != nil {
				panic(err)
			}
			defer logfile.Close()
			out = logfile
		}
		log.SetOutput(out)
	} else {
		log.SetOutput(ioutil.Discard)
	}

	p := problem{
		in:  bufio.NewReader(os.Stdin),
		out: bufio.NewWriter(os.Stdout),
	}
	p.solve()

	if err := p.out.Flush(); err != nil {
		panic(err)
	}
}

type problem struct {
	in  *bufio.Reader
	out *bufio.Writer
}

func (p *problem) PrintInt(d int) {
	p.Printf("%d\n", d)
}

func (p *problem) Printf(format string, a ...interface{}) {
	if _, err := fmt.Fprintf(p.out, format, a...); err != nil {
		panic(err)
	}
}

func (p *problem) Printfln(format string, a ...interface{}) {
	if _, err := fmt.Fprintf(p.out, fmt.Sprintf("%v\n", format), a...); err != nil {
		panic(err)
	}
}

func (p *problem) NextInt() int {
	return stoi(p.Next())
}

func (p *problem) NextInts() []int {
	line := p.NextSSLine()
	ds := make([]int, len(line))
	for i, s := range line {
		ds[i] = stoi(s)
	}
	return ds
}

func (p *problem) NextSSLine() []string {
	return strings.Split(p.Next(), " ")
}

// Next reads line and return string.
func (p *problem) Next() string {
	var b []byte
	for {
		l, pre, err := p.in.ReadLine()
		if err != nil {
			panic(err)
		}
		b = append(b, l...)
		if !pre {
			break
		}
	}
	return string(b)
}

func stoi(s string) int {
	i, err := strconv.Atoi(s)
	if err != nil {
		fmt.Println(i)
		fmt.Println(err)
	}
	return i
}