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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program main
    implicit none
    integer(8) X, i, j, ans
	read(*, *) X
	ans = 0
	do i = 1, 40
	    do j = 2, 10
			if(i**j < 1 .or. i**j > 1000) then
				exit
		    else if(i**j <= X) then
			    ans = max(i**j, ans)
			end if
		end do
	end do
	write(*, *) ans
end program main