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 Julia (0.5.0) (judge verdict: Runtime Error)

if isfile("mystdin.txt");mystdin=open("mystdin.txt","r");redirect_stdin(mystdin);end
pI(x)=parse(Int,x)
pM(x::Array{SubString{String},1})=map(pI,x)
function 素因数分解(n)
  n=Int(n)
  res=Tuple[]
  for a=2:isqrt(n)
    if n%a!=0; continue; end
    ex=0
    while n%a==0
      ex+=1
      n/=a
    end
    push!(res,(a,ex))
  end
  if n!=1; push!(res,(Int(n),1)); end
  return res
end
function main()
  x=pI(readline())
  if x<4
    println(1)
  end
  for i=x:-1:1
    k=素因数分解(i)
    if all(x->x==k[1][2],[j[2] for j=k]) && k[1][2]>1
      println(i)
      break
    end
  end
end
main()
if isdefined(Base, :mystdin);close(mystdin);end