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

x = gets.to_i


loop { d, m = x.divmod 4; if m != 0 then break else x = d end };

3.step(x ** 0.5, 2) do |k|
    kk = k * k
    break if x < kk
    loop { d, m = x.divmod kk;  if m != 0 then break else x = d end };
end

puts x