{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };

  outputs = { self, nixpkgs }: let
    system = "x86_64-linux";
    pkgs = nixpkgs.legacyPackages.${system};
  in {
    packages.${system} = {
      day01 = pkgs.callPackage ./day01 { };
      day02 = pkgs.callPackage ./day02 { };
      day03 = pkgs.callPackage ./day03 { };
    };
  };
}