#! ruby
# yukicoder My Practice
# author: Leonardone @ NEETSDKASU

x = gets.to_i

f = proc {|x, k| loop { d, m = x.divmod k; break if m != 0; x = d; }; x }

x = f.call(x, 4)

3.step(x ** 0.5, 2) do |k|
    kk = k * k
    break if x < kk
    x = f.call(x, kk)
end

puts x