error[E0463]: can't find crate for `num_bigint`
 --> answer.code:1:1
  |
1 | extern crate num_bigint;
  | ^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

error[E0463]: can't find crate for `num_traits`
 --> answer.code:2:1
  |
2 | extern crate num_traits;
  | ^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

warning: unused import: `std::str::FromStr`
 --> answer.code:7:5
  |
7 | use std::str::FromStr;
  |     ^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error: aborting due to 2 previous errors; 1 warning emitted

For more information about this error, try `rustc --explain E0463`.