let nth_prime n =
  let myprimes = Stack.create in
  let primestatus p = eratos n in
  let prime_count = ref 1 in
  for index = 0 to length primestatus do
    if primestatus( index ) == true then
    begin
      push index myprimes ;
      prime_count := !prime_count + 1 ;
    end
  done ;
  pop myprimes ;